[tor-talk] TorBrowser spoofed screen size?

Joe Btfsplk joebtfsplk at gmx.com
Thu Mar 6 19:20:15 UTC 2014

Following up on inconsistency of spoofed TBB screen sizes, shown on test 
I did more testing / checking.  Then posted comments on Trac 
https://trac.torproject.org/projects/tor/ticket/7256#comment:10 & 
comment #11.

For me, with each browser fully maximized, there's a *fundamental 
difference* in what the test sites see for "screen size" of regular 
Firefox (27), VS. TBB 3.5.2.
Same monitor, same displayed toolbars (of nearly identical heights) in 
both browsers - but vastly different "screen size" detected.

This would SEEM to make TBB users stick out like a sore thumb!?  It 
seems to be a large problem, *regardless* of the system DPI setting 
(default, or custom value).
> "Additional comment: note that at the same moment Panopticlick, etc., 
> is showing an odd screen size for TBB 3.5.2 (like 1920 x **966** OR, 
> if refresh page once, perhaps 1920 x **967**), a full screen capture 
> of the same maximized browser screen (taking up full monitor), shows 
> 1920 x **1080*.*
> The "966 or 967" TBB screen height (or whatever odd number),**turns 
> out to be** the height for the part of browser window, beginning just 
> below the browser navigation bar, down to the top of "Addon Bar."
> However, in regular Fx with exact same, similarly sized toolbars 
> displayed (as in TBB), the test sites show screen size of the **full** 
> monitor: 1920 x **1080**, not just the "usable display area" of the 
> browser pane (the part of browser window where websites actually 
> display)."
> "I see "odd" (unique) screen sizes reported / detected on browser test 
> sites, in TWO scenarios.
> 1) When Windows system DPI is set = default 96 DPI.
> 2) When system DPI is NOT the default value (many users must set it 
> larger, to be able to read screens. Ex.: both Windows' & apps' Help 
> screens, or text in browser screens (TBB).
> On browserspy.dk or others, with **Windows' DPI = 96**, AND the TBB UI 
> maximized (full screen), test sites don't show "common" screen 
> (monitor) size. They show something like 1920 x 927 - a very "odd" value.
> At same exact time, regular Fx shows "screen size" = **1920 x 1080** x 
> 24."

On 3/6/2014 8:21 AM, Joe Btfsplk wrote:
> On 3/6/2014 1:59 AM, Georg Koppen wrote:
>> Joe Btfsplk:
>>> But, EVEN WHEN  I reset my system to 96 DPI, reboot - TBB still shows a
>>> weird value - like 1920 x *933* (just an example).
>>> NO one has a screen size w/ those odd numbers.  That's the issue.
>> Yes, they should be a multiple of 200 x 100. Resizing the browser window
>> does currently not take DPI and the size of taskbars into account (this
>> is #9268). See my comment 7 there as well that was probably for you.
> Thanks Georg, but I think? we're talking about different things.
> The bug #9268 is about the size of TBB window when it's launched
> (whether it fits on monitor, etc.).
> The issue in THIS post, is the "screen size" (monitor size), that can be
> detected by sites for fingerprinting purposes as opposed to how well the
> TBB UI fits on the monitor when it's 1st launched.  Not the same things
> - though possibly ? related.
> On the browser test sites mentioned, I'm not running the tests w/ TBB
> window partially enlarged (as when 1st launches).
> But to clarify / add to your comment here, IF... one DOES run the
> browser tests w/ TBB UI in "non-full screen mode," the test sites will
> show *different* detected screen size than when it's maximized.
> And, if you zoom the TBB screen (Ctrl + scroll), the test sites detect a
> different "screen size," as well.
> Different issues than my original question on this post, but worth noting.

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