Strange you're not encountering same as I'm running the latest version of Firefox too on multiple PCs, even on my Linux machines we are seeing same quirks, and from my testing it isn't relegated to just Firefox either, IE and Edge have also been problematic.
Fully aware running and managing such a large forum/site isn't easy and appreciate all the hard work too, just miffed as to why their method of implementation causes the anomalies I'm seeing, can't recall frequenting any other site(s) that have behaved so badly. For me this problem became most prevalent about a year ago, then, I tried multiple browsers/PCs, reported the issue, created a thread on the subject but in the end, only resolve was running a blocker as suggested by others, WC is the only reason I'm running one in the first place... Nothing appears to have changed as of today, yet, upon disabling my ad blocker the annoyances of the past still rear their ugly heads.
Have no problems with ads per se but when they began to "rule the roost" of sorts causing a deviation from the sites intended purpose, that's when I took offence. Pages were slow to load, scrolling lagged severely, delays in typing (text did not coincide w/key presses), these compound the issues for those coming here in hopes of finding a resolve to their device/software woes. Hopefully they can get it sorted and we can all be happy, yeah right LOL.