I don't use Firefox a lot on the Mac, and I can't seem to replicate what you're seeing, but check if you've got Smooth scrolling enabled in your preferences..
That is the damnedest thing I've seen!
My Firefox has been doing what I described above for maybe the last year and it has annoyed me to no end.
Haven't used my computer all week, and now when I go into Firefox and then Google the search term "test" I get a page with choices, and when I use my up and down arrows the page simply scrolls up and down as has been the case since there were PCs.
I cannot recreate the issue in Firefox, but please someone come to my rescue and prove that I am not a liar!!
There *must* be others out there that have witnessed what I was seeing?
For those that haven't, basically when you would search for something in Google using Firefox, in the search results page, when you used your up and down arrows, instead of the page scrolling, you would get this grey box that would move like a cursor from search result to search result.
This was annoying as hell, because I use the up and down arrows to move the page and not toggle from search result to search results because they are different things.
Maybe a search page yields 20 results, and I want to move results results #3 and #4 to the top of my browser so I can see them more clearly. Up until this issue disappeared, I could not do that.
Has no one else experienced what I described????
I should have taken screenshots of this behavior.
It's great that it appears to be fixed, but now I am annoyed because I don't know why it is fxied and fear it may return again like a wiring problem in your car!