Re: Why can't I click on the upper tabs of all the websites I'm visiting?
That problem can be caused by the Yahoo! Toolbar that extents too much downwards and covers the top part of the browser window and thus makes links and buttons in that part of the screen not clickable.
Start Firefox in Troubleshoot Firefox issues using Safe Mode to check if one of the extensions or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox (Tools) > Add-ons > Appearance/Themes).
Don't make any changes on the Safe mode start window.