[tor-bugs] #31206 [Applications/Tor Browser]: http://ip-check.info detects browser window size with JS disabled

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#31206: http://ip-check.info detects browser window size with JS disabled
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 Reporter:  cypherpunks               |          Owner:  tbb-team
     Type:  defect                    |         Status:  reopened
 Priority:  Medium                    |      Milestone:
Component:  Applications/Tor Browser  |        Version:
 Severity:  Critical                  |     Resolution:
 Keywords:                            |  Actual Points:
Parent ID:                            |         Points:
 Reviewer:                            |        Sponsor:
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Comment (by Thorin):

 Replying to [comment:13 cypherpunks]:
 > Then why is there no option that freezes the window size?

 Because technically it was never feasible, and even if so, way too
 complex, because the browser size isn't the only thing to cause the inner
 window to change

 > It is the first time I read about this (letterboxing). Can you please
 share a link for more info?

 It's easier if you just experience it.

 Download Firefox 67+ (that's when it first landed, some fixes came later:
 e.g https://bugzilla.mozilla.org/show_bug.cgi?id=1546832 landed in FF69)
 and set `privacy.resistFingerprinting.letterboxing` -> `true` load a web
 page and resize your browser: go fullscreen, maximize, manually resize it,
 flip the sidebar open, turn your toolbar on and off. Or alternatively, try
 Tor Browser alpha. Best illustrated with a website with a dark background,
 since the letterboxing is white.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/31206#comment:14>
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