Same thing - switching back and forth between maximixed and non-maximized windows works fine everywhere I have checked. There is a bit of a usability problem on touch screens/small screens - thats a known and long standing problem. But thats unrelated to the problem you are reporting.
On small screens, or very high resolution screens you may run into an issue where all apps insist on running in the maximized mode only. They do this as they switch to “mobile mode” in such situations - its easier to use the apps on touch screens if they are maximized.
Is this resizing behavior happening across all browsers and OSes?
Skylark UI doesn’t really use anything cutting edge, most modern browsers should work fine with it. Any problem you might be seeing with the builtin android browser on old tablets is due to bad usability on touch screens - the problem I mentioned earlier. You should try with “request desktop version of this site” setting of the browser turned on. Theres not much I am able to do about this issue in the near term though.
(edit: I do use uBlock myself, and that doesn’t seem to cause any issues with the UI)