[tor-bugs] #22548 [Applications/Tor Browser]: Firefox downgrades VP9 videos to VP8 when measured performance is not enough

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#22548: Firefox downgrades VP9 videos to VP8 when measured performance is not
enough
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 Reporter:  cypherpunks                          |          Owner:  tbb-
                                                 |  team
     Type:  defect                               |         Status:  closed
 Priority:  Medium                               |      Milestone:
Component:  Applications/Tor Browser             |        Version:
 Severity:  Normal                               |     Resolution:  fixed
 Keywords:  tbb-fingerprinting,                  |  Actual Points:
  TorBrowserTeam201801R                          |
Parent ID:                                       |         Points:
 Reviewer:                                       |        Sponsor:
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Comment (by vp9):

 Replying to [comment:18 tom]:
 > A few notes. I reviewed mozilla-central and -esr52.
 Now it's time for -esr60. And -esr68 will need a new patch.
 > 0: I agree, this is a hardware fingerprinting vector (albeit a small
 one, 1 bit of info). We should set the pref either very high (disabling
 VP9 for everyone) or to 0 (enabling it for everyone). Telemetry indicates
 more users fall below the 150 fps choice than above
 Maybe, that's because it varies between 29-179 on a relatively fast CPU?
 > 1: The correct place to put prefs is browser/app/profile/000-tor-
 browser.js It's best to keep the prefs all in one place. (Also see #4)
 And revisit them during rebasing.
 > 2: Setting the pref does not enable vp9 on Android. That's probably
 fine, since all Androids will be hardcoded to false (no fingerprinting)
 and the point of disabling vp9 there is because it's not fast enough for
 phones.  (True for -central and esr)
 What do Android users think about it?
 > 3: Setting the pref doesn't enable it on Macs. Same problem, except Macs
 are hardcoded false because it spins up the fan and annoys people. (Only
 true for central) Maybe this #ifdef should be backported to esr52 for TB?
 If it is I think it should be a separate commit/patch to make rebasing
 easier (on rebase we can just drop the individual patch entirely.)
 Disabling vp9 and adding a fingerprinting vector just because of the fan?!
 Why is this true for Tor Browser?
 > 4: The benchmark is skipped correctly when the pref is set manually.
 However, setting the pref in all.js means the pref won't have a user
 value, and the benchmark will be run. That's bad, so that's two reasons it
 should be in 000-tor-browser.js
 That's bad. And the benchmark will be run on every update anyway.
 > 5: I assume, but never verified, that prefs set in 000-tor-browser.js
 are considered to 'have a user value'.
 Probably, no.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/22548#comment:27>
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