No. Could be your monitor or something? :d
Usually with firefox it's one of your addons acting up. The more of them you have, the more likely one will not be compatible with a new version of Firefox and fuck it up. Try updating them all. If that doesn't work, try deactivating all of them and activating them one by one (or in small groups) to see which causes it. Then remove it.
I had a problem with the new firefox update (tooltips not showing, and a little offwhite box showing up whenever I stop moving my mouse). That turned out to be a problem of the Google searchbar addon. I simply updated it.
Worst case scenario: try exporting all bookmarks, exporting all add-ons (there's a free exporter somewhere that exports everything, xsi's, bookmarks, settings, etc., or simply make note of them and reinstall them), and do a clean install and restore bookmarks and addons.