When I scroll on Special:Preferences, the bottom bar with the save button lags behind. I.e. when I scroll up, the bar moves up, too, and only after one second or so jumps back to the bottom. When I scroll down it vanishes and comes back only several seconds after.
I only tested with a current Firefox on a slow computer with Linux, but I assume this must be a browser issue. Anyway, I can confirm it is caused by rMWa91d95c0f107: Work around disappearing Special:Preferences buttons on RTL in Edge, the fix for T220706: Can't save preferences using microsoft edge (buttons with "position: sticky" disappear in RTL languages when using Edge): When I remove the filter: brighness(1), the bar behaves as expected. So it would be nice if that fix could be limited in some way (either via some user-agent hack to only Edge browser, or at least to RTL pages only).