Please add some system description like which OS you are using - and add a screenshot.
If you have a Display Scaling mechanism activated please try to disable that one by setting it to "100 percent" - first only in the OS and then only in the browser! And/or try a different resolution. This is not a solution but just an attempt to detect the source of the problem.
(( I am using exclusively Firefox/Librewolf on both Linux and Win11 and do not have that problem. But this does not help you, of course... ))