[tor-bugs] #5798 [Firefox Patch Issues]: Improve persistence and WebFont compatibility of font patch

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#5798: Improve persistence and WebFont compatibility of font patch
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 Reporter:  mikeperry                      |          Owner:  mikeperry
     Type:  defect                         |         Status:  new      
 Priority:  major                          |      Milestone:           
Component:  Firefox Patch Issues           |        Version:           
 Keywords:  tbb-fingerprinting, interview  |         Parent:  #7248    
   Points:                                 |   Actualpoints:           
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Comment(by mikeperry):

 From your description, it sounds like both patches are functioning
 properly for the flippingtypical test. The only thing the preferences
 system is supposed to give us is to prevent redirects/refreshes from
 zeroing the font probe list (allowing new fonts to be probed after the
 reload).

 The second site is a little concerning, but could be because we cause a
 different fallback than the generic face they expect when they hit our
 limit. Possibly a separate bug.

 However, there is a third test I'd ideally want to work here, but to be
 honest it's one I couldn't immediately find how to do in the codebase
 myself. I want webfonts *not* to count towards your total, so that if a
 website uses @font-face to source 10 remote fonts, those are not counted
 towards this limit. At first, I thought I could simply set a bit in nsFont
 when these fonts were loaded, and check for the bit in the CSS rule
 loader, but it didn't seem to be that straight-forward and/or I was
 missing some crucial detail where @font-face rules get converted into
 nsFonts.

 If you can figure out where that is actually happening, we'd pay for that
 time too.

 Note that our default NoScript configuration blocks WebFonts. You'd need
 to go into NoScript Options->Embeddings and uncheck "Forbid @font-face" to
 test.

 The PDF.JS extension (https://addons.mozilla.org/en-
 US/firefox/addon/pdfjs) is a good test. It uses @font-face internally for
 the fonts provided by the document, and most PDFs are visibly damaged by
 our font limits inappropriately applying to those document fonts.

-- 
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/5798#comment:9>
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