The default window size on my system (Windows 11), based on a screenshot I took upon opening the browser, appears to be 1002 x 1114 px.
Despite any privacy issues that may entail, I want the browser to remember the last used window size.
Is this possible?
Are you maximizing, tiling? This seems like a very strange size (assuming 1002 width and 1114 height). What do you get on TZP ?
The short answer is “No”.
The longer answer: RFP (privacy.resistFingerprinting, which is locked in future versions) will open new windows (newwin) at set sizes: generally speaking it is in steps of 100px high and 200px wide, up to a certain max width and max height. This is done to reduce the number of inner window sizes or “buckets” of users (which at the time of writing is also the outer window and screen and available screen measurements) in the Tor Browser crowd. Think of those on smaller screens being perhaps (width x height) 1000x600 or 900x600, and larger screens being 1000x900.
If we allow newwin to be remember from it’s last state, where users resize the window (even accidentally, it’s not hard to do), toggle UI bits on/off, maximize etc, then this would lessen that protection
1002 x 1114 will include the whole window, so will be partly based on the Windows 11 theme etc.
Changing privacy.resistFingerprinting to False has allowed me to save my window size, so all it sorted 
OK, so that’s your outer measurements which is about right - a little width for the chrome border + height to cover the tabstrip etc. Disabling RFP defeats the purpose of being anonymous, and as already mentioned privacy.resistFingerprinting is locked in future versions
I understand that you only want to bypass some IP blocks and don’t care about being tracked, but for readers of this forum - DON’T CHANGE about:config prefs
FWIW, TB13 has bigger real estate for newwin (1400 x 900) and for one off sites it is not problematic to go fullscreen or maximized (i.e the fingerprint of the new size is limited to those few sites for linking). There should be no reason to disable protections to get around window sizes. If you’re using TB then you help others by growing the crowd of like fingerprints - by disabling RFP you don’t contribute
A related question, if I may? Is this fully DPI-aware? If I start using TB when the display setting is say 120dpi, then if I change that to 96dpi (now we have 125% more logical pixels par inch), would that confuse TB in some way?
yes - newwin creation should get the dimensions correct, I say “should” because there have been in the past rounding errors causing a slight diff (e.g. resulting in wasting 99 potential pixels)
Thanks for clarification.