[tor-bugs] #30812 [Applications/Tor Browser]: cant modify browser default background color - about:blank, about:newtab

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#30812: cant modify browser default background color - about:blank, about:newtab
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 Reporter:  kingfitz                  |          Owner:  tbb-team
     Type:  defect                    |         Status:  needs_information
 Priority:  Medium                    |      Milestone:
Component:  Applications/Tor Browser  |        Version:
 Severity:  Normal                    |     Resolution:
 Keywords:                            |  Actual Points:
Parent ID:                            |         Points:
 Reviewer:                            |        Sponsor:
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Comment (by Thorin):

 FF75: https://bugzilla.mozilla.org/show_bug.cgi?id=1408122

 RFP off
 - using the dark theme = about:blank was still white
 - hidden pref `ui.systemUsesDarkTheme` = `1` (1 = dark, 0 = light) =
 about:blank was dark
 RFP on
 - RFP overrides prefers-color-scheme as light, and you get a white
 about:blank (i.e the above pref does not affect the fingerprint)

 Issues
 - RFP interferes
 - pref is hidden and no UI

 Solutions: as a first step
 - upstream get `about:blank` exempted from RFP - I assume this should be
 quite trivial

 Note: there's a whole string of tickets and conflicts over OS theme vs
 Firefox theme vs prefers-color and the hidden override pref: and no
 consensus.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/30812#comment:5>
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