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Full disclosure: I'm predominantly a Chrome user on Windows, but I finally let Firefox download and install the latest version, 4.0. Considering this version has been in development forever, I frankly expected better.

It appears that they've "improved" text rendering by applying font smoothing or anti-aliasing across the entire user interface—not just the text displayed on the pages themselves, but also the text in menus, toolbars, and dialog boxes. Even the context menus use a re-hinted version of Segoe UI.

I think it's blurry and very difficult to read. How do I turn it off? I can't find anything in the Options dialog that looks useful. Perhaps it's something in about:config, but I don't know enough about Firefox to know where to start looking. I can't imagine they would make such a dramatic change without providing the facility to revert to the classic rendering mode if the user so desired. Open source software is notorious for gratuitous customizability; here's a case where I would actually appreciate it.

Additionally, I've discovered that I frequently out-run its ability to process input. In every text entry field that I've come across, I've out-typed Firefox's ability to display each character. More than once, I've even managed to crash the browser trying to type, with only one tab loaded. I suspect this is related to the font rendering changes, as anti-aliasing requires more computing "umph". I'm hoping that if I find the button to turn that off, it'll fix the severe typing lag. But if anyone just so happens to have any other suggestions on how I might fix that, I'm all ears.

The machine in question is a Dual Xeon with 5 GB of RAM running Windows Server 2008 R2, 64-bit.

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up vote 6 down vote accepted
  1. Navigate to about:config
  2. Find the item labeled gfx.direct2d.disabled, and change its value to True.

This turns off hardware acceleration and should make your fonts more readable.

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Excellent, that helped a lot. (Although it's still significantly slower than Chrome, and I still see some typing lag.) Also, is this the same thing as the "Use hardware acceleration when available" checkbox under the "Advanced" tab in the Options dialog? – Cody Gray Apr 10 '11 at 5:09
I believe so. There is a rather interesting thread about this over at Mozillazine: – CGA Apr 10 '11 at 18:01
Hmm yeah, it looks like it is. And I read as much of that discussion as I could stand. It's just a bunch of uninformed people ranting and theorizing. There's no official word from any of the devs (but a lot of reasons why I prefer SE to traditional forums). If this is what fonts are going to look like now on Windows, I'm going to have to give it up completely for the Mac. I can't use WPF applications like Expression Blend for the same reason—the fonts look like crap. It's just not that hard to get font rendering right; not sure why MS has so much trouble. Nor why Mozilla has adopted it... – Cody Gray Apr 11 '11 at 8:02
Thank you very much. It now works perfectly with MacType and now I can see pretty customized font rendered text instead of ugly ClearType. Despite the question is about Firefox 4, it works for Firefox 16 as well. So thanks again! – Lyubomyr Shaydariv Oct 27 '12 at 20:35
I didn't see this option under Firefox 36.0.1 – Trevor Hickey Mar 13 '15 at 23:27

In more recent Firefox (38+) and SeaMonkey (2.35+) versions, gfx.direct2d.disabled has nothing to do with HW acceleration with regard to fonts display. Instead, you may need to set layers.acceleration.disabled=true.

Additionally, it may be your graphics card driver settings which cause your fonts to look anti-aliased. See this question for more details.

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