> You switch from spotlight to Firefox, there's the wheel; leave computer alone for sometime and comeback there's the wheel.

You are definitely not alone:

https://bugzilla.mozilla.org/show_bug.cgi?id=1979283

https://bugzilla.mozilla.org/show_bug.cgi?id=1982717

https://bugzilla.mozilla.org/show_bug.cgi?id=2002102

https://bugzilla.mozilla.org/show_bug.cgi?id=1995973

https://support.mozilla.org/en-US/questions/961898

While there are a few overlapping/similar issues being alluded to in those threads, it definitely seems like something is going on re: task switching. There are also a couple of tricks mentioned that might fix some specific issues related to bookmarks or graphics acceleration, but no silver bullets so far.