The default Tor windows size (500x1000) I find too small and I would like to make it bigger. I understand that making Tor full screen is dangerous, as full screen resolution is device dependent, allowing me to be fingerprinted.
However, is it safe for me (i.e. fingerprinting resistant) to drag the lower right hand corner of the window every time I start up Tor, resizing my window to something a bit smaller than fullscreen, which is different from Tor defaults but varies every time?
Yes, it is harmful for the duration of the window at that size.
Specifically, manually resizing it will create a very unique fingerprint for your window size, which will persist until Tor Browser is reset to it's chosen size.
This would make it easier for advertisers to track you across tabs and websites.
You'd also be in a small set of users who did use some obviously not automatic window size, and would potentially link you between session of different manually resized windows, since your window size is always a strange non-standard number. This might allow a careful observer to link your activity across multiple sessions and identities together.
From the version 9 of Tor browser, you can resize painless the window, because they introduced a new anti-fingerprinting technique called letterboxing from firefox 67. Letterboxing adds margins around the content view of the window. Here the complete story: https://bugzilla.mozilla.org/show_bug.cgi?id=1407366
If you change your screen resolution to something smaller, then the browser window will appear larger on your screen. This will still send the same browser window size to the websites you are browsing, but will let you see things more clearly.
Yes, it will allow you to be tracked easier, if you really need to change the size, make sure you keep changing it every single time a page loads.
