new windows (on startup, on new identity, via menu>new window) on creation only (i.e you can resize, maximize, fullscreen afterwards) will always open in certain size steps under a maximum width/height - the largest each can fit on your avilable screen
width steps in 200’s, height in 100’s - and the default maximums are as follows
these prefs are hidden by default - i.e you need to create them in about:config - but changing them can result in your fingerprint being different
e.g. if set them as 1920 + 1080 - then your window might open at 1900 wide and 1000 height (depending on your toolbar taskbar height) if you have a screen that is 1920x1080 or higher
this would make your fingerprint pretty much unique among Tor Browser users - so we don’t recommend users change any settings/prefs for this reason
What is it you’re trying to achieve here, and can I ask … WHY? knowing why might help us to make it better
I’m quite convinced my requirement is very unique and specific. I mostly use Tor on a specific Website, which works best in a specific window size. Laziness weights more in my specific case than fingerprints.