Nothing to do with the new Hide post feature.
I didn't think so, but I noticed it on that one first.
Happens when you zoom or use custom fonts size.
Zoom is default 100%, no custom font size.
Clear your cache to make sure it's not some obsolete css settings.
Happened on two different legacy Firefox browsers. Restarted Waterfox, same thing happens in both normal and in-private.
Cleared all data in Waterfox, restarted, still persists.
(post is archived)