[tbb-bugs] #31887 [Applications/Tor Browser]: maximize warning panel entropy: can reveal app locale

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#31887: maximize warning panel entropy: can reveal app locale
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 Reporter:  Thorin              |          Owner:  tbb-team
     Type:  defect              |         Status:  new
 Priority:  Medium              |      Component:  Applications/Tor Browser
  Version:                      |       Severity:  Normal
 Keywords:  tbb-fingerprinting  |  Actual Points:
Parent ID:                      |         Points:
 Reviewer:                      |        Sponsor:
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 I actually thought this had been addressed years ago (maybe it was?) but
 something nagged me so I did a full test, and added the PoC


 **Note**:
 - In #31598 when LB (letterboxing) is enabled, the warning panel is not
 used
 - `extensions.torbutton.maximize_warnings_remaining` cannot be `0`
 - user has to initiate FS (I could cover the entire page with an element:
 but they still have to click it)
 - it only affects *some* locales, not all (but are the others robust to
 future changes?)
 - so effectively the risk should be fairly low, but then I can also see a
 lot of users disabling LB (unless we do a better job of educating them:
 see solutions), so the risk is higher (for those exposed)

 **PoC**
 - https://ghacksuserjs.github.io/TorZillaPrint/TorZillaPrint.html
 - just click on the full screen test
 - let the page load first: I had one test where the connection was a bit
 slow and I clicked too early, and it was all a bit laggy, and I got back
 418 pixels. I could fix that by waiting a little longer to grab the second
 value, but not today.

 **Observations**:
 - `ja` and `ka` are unique
 - `ar`, `fa`, `ko` and `zh-TW` create another bucket
 - `mk` I can't test (#31725), and `ko` needs to be confirmed (#31886)
 - Can we rely on previous chrome styling to remain consistent: see the
 ESR60 `ka` was `42` pixels like most other languages, but it did not
 migrate to `40` pixels in ESR68 like most other languages.

 **Beware**:
 - I only tested at default 1000px width. The length of each localized
 message is not the same, so smaller windows (e.g on smaller screens: are
 there any?) would provide more entropy, as some would invoke a second or
 third line and others not.
 - Similarly, if users resize the browser, some 2-liners will become one
 while others won't: but users should not resize the browser unless they
 have LBing (in which case, the warnings are disabled)

 **Obligatory Pic**:
 - see attachment: The ESR60 based ones are for nostalgia's sake, as I
 upgraded my language test suite :)

 **Possible Solutions**:
 - lock the LB pref in the future
 - make the warning panel the same height somehow: e.g just force it to be
 100px high or something.
 - ditch the panel UX (or enhance it?) and use a different medium: end-user
 education: I have some other ideas but no idea how feasible they are, and
 they tie into informing the user about LB'ing/resizing/maximizing/FS: all
 in one hit

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/31887>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
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