Tor Browser detected screen size is different than Firefox
Now using TBB 3.5.2 (Windows). I see "odd" (unusual) screen sizes reported / detected for TBB browser tests - at several sites (browserspy.dk, panopticlick, ip-check.info). Like showing 1920 x 966 (or 963,etc.). This stands out like a sore thumb. It is also affected in Windows by 2 system settings.
- When Windows system DPI * IS * set @ default 96 DPI.
- When the system DPI is NOT the default value (many users MUST set DPI larger, to read various screens. Ex.: both Windows' & apps' UI & Help screens, etc.
With system DPI @ 96. At the same time as testing TBB, regular Fx (no "privacy addons" hiding / spoofing browser data), all the test sites show 1920 x 1080 for Fx.
That is w/ EXACT same toolbars & other UI elements displayed in both browsers, where test sites show odd values for TBB - 1920 x 966 (or what ever). Not good.
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 , 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).
2nd Case: When system DPI is NOT at default 96.
Not sure anything can be done, so sites monitoring screen size (TBB or any browser) don't see odd sizes, when the system DPI is @ NON-default value? But, even in that case (say, DPI - 110), the test sites STILL show different screen sizes __for TBB vs Fx __(27). So all Fx & TBB users that set the system DPI @ 100, 110..., sites that check will see different values for TBB vs. Fx. Again, not good.
See comments 10 & 11: https://trac.torproject.org/projects/tor/ticket/7256#comment:10