456356 - Uneven kerning with non-antialiased fonts/text

Status: UNCONFIRMED

(Firefox :: Shell Integration, defect)

Description

[Tibor Ébner]

User-Agent:       Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.5; hu; rv:1.9.0.1) Gecko/2008070206 Firefox/3.0.1
Build Identifier: Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.5; hu; rv:1.9.0.1) Gecko/2008070206 Firefox/3.0.1

Firefox displays non-antialiased text with weird, improper kerning that is different from the one used in native OS X applications (e.g. Safari). Safari/OS X seems not to use kerning at all with anti-aliasing switched off below certain pixel size in the System Preferences. Nonetheless, Firefox 3 tries imposing some sort of kerning on these fonts as well, even in the case when browser.display.auto_quality_min_font_size parameter is left in its default state, in other words, Firefox 3 doesn't respect the aforementioned parameter in OS X (in Windows XP it does, however). The real problem is that whatever kerning Firefox uses, it is wrong by the first inspection: uneven kerning, legibility issues, ugly overall look. Firefox should either respect the advanced font rendering parameter, or at least use correct kerning information (like TextEdit does, for example).  

Reproducible: Always

Steps to Reproduce:
1.Turn off anti-aliasing in System Preferences/Appearance for font sizes e.g 9 point and smaller. 
2. Browse to the same page (containing considerable amount of text) in Firefox 3 and Safari 3.  
3. Decrease font size in both browsers to the same value, a value where anti-aliasing is not used any more (9 in our example).

Actual Results:  
Firefox displays ugly looking text with unreasonable kerning while Safari renders text as it should.   

Expected Results:  
Firefox shouldn't impose kerning on fonts when it's expressly prohibited in a config parameter. Otherwise, Firefox should render text with an acceptable overall look, matching native OS X applications' text rendering output (e.g. Safari 3)

Comment 1

[Tibor Ébner]

Attachment: An example of the text rendering issue at 9px font size.

Comment 2

[Tibor Ébner]

To have Firefox 3 adhere to system anti-aliasing settings set gfx.use_text_smoothing_setting to true (in the "about:config" page).

Comment 3

[John Daggett (:jtd)]

Safari doesn't do kerning (at least not yet).  Even without kerning, we'll be using non-pixel aligned advances so simply disabling kerning in some situations is not the complete solution here.

Comment 4

[Robert O'Callahan (:roc) (email my personal email if necessary)]

Attachment: testcase in a real image format

Comment 5

[Robert O'Callahan (:roc) (email my personal email if necessary)]

We seem to be honouring the system AA settings just fine with gfx.use_text_smoothing_setting set to true, after the browser is restarted. (I don't know why that isn't the default, but that's probably fodder for a different bug.)

We could use more details about the original bug here, such as the exact font in use and a screenshot of Firefox vs Textedit (as John noted, Safari doesn't do kerning). However, when I bring up Verdana 12px, with AA disabled for fonts of size 12px and below, I see that in "Hello" there's only a 1px gap between the 'e' and 'l' in Firefox, but a 2px gap in Textedit. That is probably a bug.