Firefox problem

[Coldicote]

I recently started using Mozilla Firefox and was getting along fine with it until something went wrong. When I tried to open Firefox it played tricks with my computer screen, jumping from a full screen view to a smaller partial screen view with a black area all round the edge. I uninstalled Firefox, re-started my computer, re-installed Firefox and tried again but the same thing happened. So I've given up and uninstalled for a second time. I've run System Restore as a precaution and am now back to square one with Internet Explorer. Can anyone please suggest what might have caused the problem?