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How to enable typographic (kerning, ligatures) improvements in iceweasel?

Asked by [ Editor ] , Edited by Helmut Grohne [ Editor ]

For some time now Firefox provides visual improvements to font rendering as described on I have seen this work on a Debian Lenny system reading The difference was easily to be spotted with “fi” ligatures. Now how do I enable this on sid? Some first googling revealed that browser.display.auto_quality_min_font_size is involved, but lowering it did not give the better rendering.

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1 answer


adam.trickett [ Editor ]

I don’t know about SID, but Iceweasel in Squeeze follows the rules as described here:

and the browser.display.auto_quality_min_font_size option does work.

According to this article all 3.x versions should honour this command. Versions based on Gecko 2.0 and later (FF4) doesn’t need this as it’s font rendering is so fast that there is no speed advantage in disabling it.

However it does require the font that you are using on the page to have the built in bits to support all the extra features, and I don’t think many older fonts support these features.

edit: If you are looking at a web site that doesn't specify a font then your browser will use it's default font which may not have the features required - you probably want to set your default font to one that does, e.g. Dejavu.
NN comments

First of all the improved rendering works on the site. However it still does not work on Maybe some font packages are missing? Any guesses? ;–)

I’ve just had a look at the style sheets that these sites use.

The mozilla site uses a style sheet that specifies a series of fonts. If they are installed on your computer and have the various features enabled then it will work.

Lwn doesn’t specify a font of any kind so it will use your browser default. If you have set a browser default that doesn’t have the right features then it won’t work. You can change your default, so it’s worth trying different defaults to see if that changes the way fonts are rendered on the Lwn site. I told my Iceweasel to use MS’s Verdana and that is sufficient to work properly.

From what I understand (and I’m no expert) you need a modern font, often a .otf not an old .ttf if you want it to work. In the Mozilla example they use Dejavu serif which from my Debian Squeeze system does work fine.

I’m sure a font expect can tell you which fonts will do the trick and which wont. I suspect that many modern commercial ones and free ones where the creator cares will work but a lot of older and give-away fonts won’t work. I don’t know about postscript fonts so I can’t comment.

.trickett Thank you very much for this excellent comment. This sid box was originally installed as Potato (no joke), so the old defaults probably carried along. The default font was called “serif”. Changing it to “DejaVu Serif” did the trick (i.e. has the better rendering now). Maybe you can update your answer to suggest changing the default font?

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