Tor window size leaks information
Tor's default browser size is too small and resizing can leak information, because resizing to a common internal window size is difficult. The window size quantizing that tor browser does/used to do (I can't get it to work in this latest version, 7.0.7) was never very good anyway, and typically resulting in fairly unique fingerprints as per EFF panopticlick.
A workaround is to somehow get the internal window size (the size of the content window, sans toolbars and etc), and make it a common monitor resolution by resizing the window to that size + the size of the toolbars, for example I have been using:
until xdotool search --name "About Tor - Tor Browser" windowsize 1920 1183 ; do sleep 0.5; done
on tor browser startup which gives me an internal window size of 1920x1080, which panopticlick says has only 2.44 bits of identifying information (1/5 browsers share this value, supposedly).
However, this is fragile, and minuscule changes to font rendering settings that change font sizes by so much as a pixel can completely throw this off and result in an extremely unique browser fingerprint.
I can think of a few ways this might be solved, some of which may work in combination with each other:
- Have a setting in Tor Browser for a fixed content window size, which will resize the whole window to fit
- Have some kind of prompt for the user to choose between common browser content window sizes (is there information anywhere on which sizes are the most common?)
- Default to the largest common browser window size, and on resize snap the window size to other common browser content window resolutions
Most of these involve knowing ahead of time which browser content window sizes are common however, which I couldn't find online.