The Double-Edged Sword of the Web

A couple of weeks ago I had some time in my hands and decided to fix cross-browser rendering issues for Pony Foo. The ensuing bug hunt was a good reminder of just how obnoxious web development can get, in spite of that same obnoxiousness being the main driver of the web’s success as the greatest platform that is, as Xaro Xhoan Daxos would put it.

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Nicolás Bevacqua
| 16 minute read | 13

Pony Foo is a web development blog. As such, visitors are mostly privileged web developers using macOS and Google Chrome. Here are some historical stats, pulled from Google Analytics:

  • Over 37% of visitors are on a Mac
  • Under 34% of visitors are on Windows
  • Over 72% use Google Chrome
  • Roughly 10% are on Safari, and another 10% are on Firefox
  • IE and Edge, combined, amount to barely over 1% – at 0.84% and 0.3%, respectively

The fact that people were seldom using anything other than Chrome gave me a good cover story for not pouring any effort into resolving long-standing (albeit minor) CSS rendering issues in Firefox and Safari. However, 20% of visitors were getting a less than ideal experience, which ultimately wasn’t something I could scoff at. Furthermore, it didn’t speak well of me to have these blatant rendering bugs lying around in my blog when visited through popular non-Chrome browsers. It wasn’t tidy.

In this article I’ll go through the bugs I fixed for Safari and Firefox visitors, outlining the problem, possible solutions, and how I ended up fixing them. As it turned out, not all of the bugs had a simple fix, and that’s the largest reason why I neglected fixing them for so long, as we’ll go over while analyzing each specific bug.

Besides the specific instances of cross-browser issues I detected and fixed, we’ll also be discussing the impact of having to deal with heaps of different rendering engines, when it comes to web development in general as opposed to mobile application development. In that regard, this article follows up on what Eran Hammer wrote about the web last month: “The Fucking Open Web”. While under a belligerent light, Eran’s article highlights the challenges of web development when it comes to building a polished web application that performs well under the most popular runtimes – and there’s a lot of them, what with Chrome, Firefox, Safari, IE, Edge, Mobile Safari, and (let me know when to stop) developer editions such as Chrome Canary, Firefox Nightly, Rockmelt, Electron-based browsers, crawler bots, RSS readers and other niche browsers – all of them serving one purpose or another, and application developers being judged as the ones at fault when a cross-browser API inconsistency causes our websites to fail under a particular set of conditions.

Here’s one of those niche browsers – which by the way, looks freaking gorgeous! 🤓

The Web Wields a Double-Edged Sword. ⚔

On the one hand, having a diverse choice of runtimes allows for the web’s user base to pick their favorite in terms of customization, tabbed view management, privacy settings, and so on.

That same plurality prevents a single company from controlling the web platform.

There’s no gated access to web publishing, no app stores, and we have a seamless “installation” process that’s so lightweight – in comparison – that we can afford to go through it on every visit to a site.

Competition keeps the web platform a vibrant one, we have so many features and upcoming features being worked on that no single person truly knows the full stack. They may understand the big picture, as we do, or they may be very well versed in a particular aspect of the platform, such as SVG, WebRTC, ServiceWorker, or accessibility.

Not being proprietary, the temptation a single company may have had to introduce breaking changes into the platform every other year never had a place in the web, which still retains the ability to render decades-old websites.

On the other hand, individual browsers with significant market share are company-owned and drive the web in terms of specification and implementation. Sometimes, browsers disagree about features before they’re specified, resulting in different implementations. Naturally, bugs can also be a source of divergence across browsers.

Different browsers have different bugs, resulting in libraries like jQuery or normalize.css being highly valued for their convenience when it comes to developer productivity and not having to deal with the nuisance that is cross-browser development. This deficiency in productivity when developing applications that are meant to run on a diverse set of consumer devices and browsers, and not just one or two devices and a single browser in controlled environments – such as an enterprise application for companies mandating use of Internet Explorer – is for the most part what Eran alludes to when he writes “putting together a great [web] experience [is] too fucking expensive”.

Let’s take a look at the concrete examples of cross-browser development issues I ran into and fixed (to some extent) for Pony Foo.

CSS Element Outline in Firefox

Pony Foo uses the CSS outline property to draw attention to focused elements. The following picture displays three different links and a text input, all of them focused – under Google Chrome. The article title outline felt particularly clever when I first implemented it. It’s a thick dotted outline with an artistic feel to it, yet it was relatively easy to achieve in CSS.

CSS outline on Pony Foo elements under Firefox
CSS outline on Pony Foo elements under Firefox

At some point in time, it was pointed out to me that Firefox renders outlines quite differently. My clever article title outline trick didn’t look so elegant in Firefox. They have a different opinion on how to render outlines when it comes to multi-line text. I didn’t include the input in this screenshot, but suffice it to say that the outline is rendered outside of the input instead of within. Elements with :before or :after pseudo-content are taken into account while drawing the containing element’s outline, even if the pseudo content itself is absolutely positioned. In soviet Firefox, element outlines you.

CSS outline on Pony Foo elements under Firefox
CSS outline on Pony Foo elements under Firefox

The most commonly proposed fix to Firefox’s outline bug when dealing with absolute positioned pseudo content is to ditch outline entirely, and to use box-shadow instead. While such a fix is mostly a drop in replacement in some scenarios, it’s pretty hard to draw a dotted outline using box-shadow. Not impossible, you can do all sorts of things with box-shadow, but definitely not a trivial thing to implement.

Having neglected this bug for so long, I felt uneasy about switching to box-shadow just for 10% of my visitors, so I waited it out. When it came to deciding how to fix it, I decided not to. I took the liberty of using a user-agent detection library – I know, how dare I? and then created my first hacks.css stylesheet.

.ua-firefox * {
  outline: none !important;

Oh, well.

At times it’s important to remember that websites don’t necessarily have to look exactly the same on every browser. Other than web developers, humans have little interest in that. Humans will seldom use different browsers. Unless there are gross differences across browsers, like using entirely different sets of font faces, humans are not going to care. We need to learn to let go. User-agent detection might not be the prettiest practice in our toolset, but it is available for us to temporarily patch over these kind of problems. While, yes, no outline is bad user experience, a misdrawn outline is even worse. I’d rather have no outline for Firefox-wielding humans than have the hideous “a two year old kid drew all over my article’s title” type of outline pictured above.

It’s all in the gradual improvements.

“Dotted” Borders as a Design Tool

Pony Foo is a colorful place on the internet. On the home page, you are greeted with headlines for each article, each using different colors. To render this playful aspect of Pony Foo’s design, I’ve experimented for quite a bit before settling for border-top: 9px dotted $COLOR rules. This looks super pretty on Chrome! The squares shown below don’t really convey a “dotted” style when the border is this thick. At a width of 1px, however, the intermittence of the border does tell a “dotted” story. As the border grows in thickness, though, the “dotted” story dilutes into an unspoken “squared” border style.

Dotted border style in Google Chrome
Dotted border style in Google Chrome

At some point, it was pointed out to me that Firefox and Edge use, well, dots. Presumably, this was done so that the dotted border style is actually “dotted”, regardless of thickness. Frankly, it just doesn’t look as pretty for my use case. It’s not the design tool I leveraged. Not anymore. It’s something entirely different. Of course, Firefox and Edge are not to blame here. Or are they? Of course not. In any case, there’s a discrepancy between Firefox, Edge, and other browsers. One that makes the site look pretty poorly designed on Firefox and Edge.

Dotted border style in Firefox
Dotted border style in Firefox

I wanted to preserve my “squared” borders in Chrome et al. This was a Firefox/Edge problem, not something that’s easily patched with one of user-agent sniffing or deprecating the design for every other browser. Eventually, I settled for an outset border style when a Firefox or Edge user agent was detected. This allowed me to introduce minimum changes to my CSS code base, while fixing the not-so-good-looking dotted border style in Firefox and Edge, and preserve my existing styles in other browsers.

.ua-firefox .dc-colored,
.ua-edge .dc-colored {
  border-top-style: outset;

Again, websites don’t need to look the same, all the way down to pixel perfection, on every browser. Otherwise, what good is progressive enhancement? Have we been lying to ourselves all this time? No. Different browsers. Different purposes. Different looks. It’s obvious, once we let go of these terrible mantras.

Solid border style in Google Chrome
Solid border style in Google Chrome

If you’re curious about how I do user-agent detection in my Express app, here’s a code snippet you can use as a middleware. Once you have that code in your app, all that’s left is injecting req.ua into your views. In my case, I prefix req.ua with ua- and inject that into my <html> elements.

import { parse } from 'useragent';

export default function sniffUserAgent (req, res, next) {
  const nonalpha = /[^a-z]/g;
  const agent = req.headers['user-agent'];
  const { family } = parse(agent);
  const ua = family.toLowerCase().replace(nonalpha, '');
  req.ua = ua;

Oh, and you’ll need to npm i -S useragent.

Tables in Firefox and IE

Pony Foo uses display: table in quite a few places. One caveat when rendering tables in Firefox and IE is that max-width rules can be ignored by the rendering engine if they are contained within tables without table-layout: fixed. As it turns out, the specification is on Firefox’s and IE’s side for this particular inconsistency. Who is correct isn’t important. What should be important is that browsers put consistency across themselves first. Consistency across browsers should be the most sought-out aspect of feature development.

Yet, consistency is consistently not attained. It’s sometimes more interesting to work on new features than to fix existing issues on the underlying platform, some of these inconsistencies have been neglected for years. Reporting them time and again to browser vendors could mitigate their impact (by having them patch the features), to the extent that they’re willing to prioritize those fixes over newly developed features.

Oh, look! A composite worker! *Rushes to drool all over it.* 🤓💦

Line Height in Firefox

This one reminded me that even when we leverage libraries meant to ameliorate the effect of inconsistencies across browsers, some of them might still slip through the cracks. In this particular situation there were a few text inputs that were misaligned with their accompanying buttons roughly by one pixel. Upon looking into the issue, it turned out that Firefox had a line-height of 19.45px whereas Chrome and others used 18px.

Presumably, this issue arised from differences in how different browsers calculate the default line-height value for elements. I didn’t care enough to dig deeper into the issue than that. Sometimes, this is okay too.

Background Gradients in Safari

Headlines on the home page use a gradient between the background color and transparent to overlay a preview image into the content without introducing a hard break between the content and the image. This saves room and allows me to introduce a revealing effect by adding a transition on opacity when the element is moused over.

A background gradient in Google Chrome
A background gradient in Google Chrome

Some helpful soul sent me an email telling me that the gradient was “broken” in Safari. Upon inspection, it turned out that Safari dislikes the transparent aspect of the gradient, for some unspoken reason. Luckily, a fellow Stack Overflow user noted that using rgba(0, 0, 0, 0.00001) instead of transparent would get the job done and avoid rendering issues.

Weirdly enough, they ran into the issue under Chrome and not Safari, whereas I was able to reproduce it in Safari but not in Chrome.

A different time, a different king.

A background gradient in Safari
A background gradient in Safari

Okay, I promise there’s only one bug left for us today.

Relative <svg> URL Strokes and the Phantom of Animation

This was one of those “I can’t believe this ever worked” type of bugs. I noticed that the following <svg> graph wasn’t rendering the page views plot line on Safari. After running into a wall for several minutes, I figured out that the stroke for that plot line was a relative URL: stroke: url(#sg-pageviews-gradient). This was being set on the CSS stylesheet. A URL in an stylesheet is relative to that stylesheet.

A graph of subscribers and page views over time
A graph of subscribers and page views over time

I have no idea why this did work on Chrome, but moving the stroke property away from the CSS stylesheet and into JavaScript code, assigning it to the <path> element as an attribute, fixed the issue. Inconsistency across browsers, again.

At the same time this bug kind of reminded me of the weirdest bug I’ve ever come across, also related to <svg>. In that article, I go on to describe a rendering bug that depended on so many conditions that I completely lost my sanity for a whole day.

Words on RSS

RSS was sort of an special kind of “bug” I had, where I had simply forgotten to include style information in my feed items’ HTML. This caused a plethora of rendering inconsistencies between the actual site, the feed’s contents, and what humans expected to see. Always inline style information in your RSS feeds.

Sure, readers may ignore them entirely, but at least you’ve tried. Pony Foo Weekly renders quite decently on Feedburner, for example.

The Fickle Nature of User-Agent Detection

All of the bugs presented so far go to show two things.

One, browsers are still as inconsistent as ever, if not more so. There is no end in sight for this plight, as browsers keep on piling more features and knowledge is further specialized and bucketed so that no single person understands the whole thing in depth. This is the biggest source of friction when it comes to developing applications that simply work across browsers: some inconsistencies may be ironed out, many others will be take their place. Web development is going to stay cumbersome for the foreseeable future.

Two, and this is not something that follows from the bugs I found and patched, but more of a realization. Yes. User-agent sniffing is evil, bad, unsophisticated, inelegant, an oft-overused, misleading band-aid. But, user-agent sniffing does serve a purpose. Snuffing out browser-specific bugs that cause rendering anomalies – while a fix is being worked on or thought up – is laughably easy when you allow yourself to leverage user-agent information, despite the heaps of advise on how user-agent detection is evil. Under the right circumstances, even goto and On Error Resume Next have useful applications.

That’s not to say you should patch all the things over with a user-agent-sniffing self-!important rule and call it a day. It’s a tool, like any other. You may use it, but you should always ping your best judgement first. It may be a good idea to have a hacks.css stylesheet where you keep track of every single awful hack your site leverages, so that you can readily identify them all, and slowly pluck them away from your site as you find more engineeringly-sound solutions.

Preferrably, ones that don’t include the made-up word: engineeringly.

So, Native Mobile Apps?

Well, yes. If all you care about is optimal developer productivity, you’ll never ever attain that in web development. That’s the price you pay for having an application that runs on the world’s largest runtime platform, that’s able to fend off against half a dozen rendering bugs and still display a somewhat usable experience to the humans visiting your corner of the internet. That’s the price you pay for not having gated access, for not having to deal with arbitrary rules imposed upon you whenever you publish an update to your application, for having a choice when it comes to where and how your application can run.

And, no. Do not give me that bullshit about Android or iOS being easier to develop for because they’re single platforms. Nothing is stopping you from sniffing user-agents, developing for a single browser, and blocking all the rest with a big fat “Your browser is not supported” notice, as bad as that’d be. How is that any different from developing for a single mobile operating system? Well, it’s different in that at least on the web you don’t have to put up with App Stores, a proprietary API, breaking changes, or licensing fees.

So, native mobile apps? No. Not fucking native.

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Comments (13)

Bruno wrote

Not fucking native! 👏

Christof wrote

seems browser sniffing is not needed always for the above examples, please see


for a Trial to get squared “dotted borders” for any browser (works in Edge, Firefox, Chrome, not tested on Safari but even works in IE ;).

Browser sniffing had so many Problems in the past (IE/Edge were treated especially bad) it just feels so wrong.

Please let me know what you think of the border solution, thanks!

Nicolás Bevacqua wrote

Great solution. Will peruse! Thanks. 🎉

Andrew wrote

You make it sound like Chrome is always perfect and the other browsers are doing something wrong. In the case of the square vs. dotted borders (“I wanted to preserve my “squared” borders in Chrome et al. This was a Firefox/Edge problem”) you have two browsers that render “dotted” borders as dots but then complain that they’re not square (interesting that all of the browsers conforming to your ideal use the same base rendering engine). If Chrome rendered the color blue as red, would you complain that Firefox and Edge didn’t maintain the redness of your blue like Webkit and it’s derivatives do!?

For what it’s worth, the dotted borders look a lot better than the erroneously-squared border anyway. if Firefox and Edge created squares but actually spaced them evenly instead of jamming the squares together at the edges, would you complain that "only WebKit-based browsers “properly merged the endpoints into rectangles”?

For years, designers only included -webkit prefixed CSS in their stylesheets because it worked fine in their browser, and now we have a state where other browsers are supporting -webkit prefixes just to deal with the selfish (and/or ignorant) attitude of those designers.

Should Firefox and Edge really start reinterpreting “dotted” as “squared” (for example) just because the (currently-) most popular browser does? And if that’s true today, then why didn’t it apply to IE’s “broken” interpretation of the CSS box model a decade ago (which, BTW, now seems like it was a good idea after all, as evidenced by the proliferation of box-sizing:border-box !)?

Then you have the nerve to say “As it turns out, the specification is on Firefox’s and IE’s side for this particular [table layout] inconsistency. Who is correct isn’t important. What should be important is that browsers put consistency across themselves first. Consistency across browsers should be the most sought-out aspect of feature development.”

Do you know how consistency is achieved? Through standardization. Who is correct is not only, important, it’s the only thing that’s important.

If you’re going to complain about browser inconsistencies, then blame the culprits instead of the innocent (or even righteous) bystanders.

Nicolás Bevacqua wrote

Nice rant but as I repeatedly outlined in my article, these weren’t issues specific to any one browser. I simply portrayed the facts from my perspective as a web developer who uses Chrome daily to test things out. In the specific case you mention, about the dotted vs “squared” borders, I make it pretty clear that while the squares are probably not what the browser should be doing, they served a design requirement I had.

As the border grows in thickness, though, the “dotted” story dilutes into an unspoken “squared” border style.


At some point, it was pointed out to me that Firefox and Edge use, well, dots. Presumably, this was done so that the dotted border style is actually “dotted”, regardless of thickness. Frankly, it just doesn’t look as pretty for my use case. It’s not the design tool I leveraged. Not anymore. It’s something entirely different. Of course, Firefox and Edge are not to blame here.

So, again, read the article. We’re saying the same thing.

manuel wrote

You just broke keyboard navigation for Firefox users on purpose? :) Never outline none! http://www.outlinenone.com/

Try instead something like: .ua-firefox a:focus { outline: 3px dotted #ccc !important; } /* kbd / .ua-firefox a:hover, .ua-firefox a:active { outline: 0 !important; } / mouse */

Šime Vidas wrote

One options is to use a library like what-input, which dynamically shows focus rings when keyboard events are fired, and hides them for mouse/touch. Seems to work great on one of my sites.

Nicolás Bevacqua wrote

The keyword is temporarily. All the issues I mentioned and patched above have been fixed in more permanent ways, my hacks.styl is empty these days! 😅

Andreas Sander wrote

Thx for this interesting “behind the scenes” article about this site and the revealed bugs. I came across this transparency bug myself a few weeks ago.

In general — without any founded reasons — in my opinion Chrome sometimes seems to add a bit more to a feature as the specification provides or it doesn’t — as all the other browser vendors are doing in one or other case — don’t follow the spec completely.

When you’re mostly developing in Chrome you are getting super fast used to these nice “gifts” Chrome gives us developers. And in my opinion this can’t be good for us or for the web because we take things for granted which aren’t. Of course browser vendors should have a consensus about the spec and the features, but they shouldn’t add extra features on it which aren’t in the spec (e.g. as the squared “dotted” borders).

All in all: Thx for this article.

kl wrote

If you’d like a fix for the transparent issue: instead of rgba(0,0,0…), use actual color with 0 opacty: rgba(255,200,100,0.00001). Some browsers naively blend colors (not in premultiplied space) and will blend with black, so you get gray in the middle.

Re: consistency, it seems like the spec + Firefox + IE are consistent, so Chrome’s behavior has been outvoted here.

Rimantas wrote

I will take my “Proprietary API” vs. “no API” any day. And “breaking changes” as a con for native? Below this article? Give me a break.

Brett wrote

License fees, breaking changes, and app stores. Those are all big pain points when it comes to releasing natively. Web can’t do everything, but it’s getting closer every day. Also, where does your “No API” come from? The W3C has released several API’s for the web.

Rudolf Olah wrote

A little disappointed that Firefox seems to be lagging behind. I’ve been using it a lot more and it’s always been my favourite browser but I had forgotten that cross platform testing doesn’t mean just testing in Chrome on multiple platforms. It’s easy to be lazy when you don’t have to support older browser.

Firefox is still a heavy hitter as far as I’m concerned; even if it looks like there’s fewer people using it, it might be the case that a website just looks bad in Firefox and they switched to Chrome to view it.