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Re: [tor-bugs] #33534 [Applications/Tor Browser]: Review FF release notes from FF69 to latest (FF73)
#33534: Review FF release notes from FF69 to latest (FF73)
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Reporter: pospeselr | Owner: pospeselr
Type: defect | Status: assigned
Priority: Medium | Milestone:
Component: Applications/Tor Browser | Version:
Severity: Normal | Resolution:
Keywords: | Actual Points: 12
Parent ID: | Points:
Reviewer: | Sponsor: Sponsor58-must
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Comment (by Thorin):
Replying to [comment:6 pospeselr]:
> {{{
> 74:
> TextMetrics interface updated, canvas fingerprinting?
> - https://bugzilla.mozilla.org/show_bug.cgi?id=1102584
> }}}
https://ghacksuserjs.github.io/TorZillaPrint/TorZillaPrint.html#fonts -
see the textmetric entry and click the view details
RFP doesn't protect against this. The prefs (all added in 74+) are
- `dom.textMetrics.actualBoundingBox.enabled` FF74+ default true
- `dom.textMetrics.baselines.enabled` - 76 Nightly still at default false
- `dom.textMetrics.emHeight.enabled` - 76 Nightly still at default false
- `dom.textMetrics.fontBoundingBox.enabled` - 76 Nightly still at default
false
measureText uses floats (which may be affected by OS), so the precision is
much higher than say domrect (which uses app-units - e.g. 1/60th of a CSS
pixel). Additionally, text layout goes from device pixels (which _are_
affected by DPI) to CSS pixels: so it could also be affected by DPI (but
no one knows for sure)
I'm not sure if it really adds any more entropy than other font
measurements like dcf's unicode glyphs - but it is another avenue
--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/33534#comment:7>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
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