Never had a serious problem with any previous version of Firefox. Since upgrading to 4, I get (Not Responding) regularly when attempting to load pages on many websites that I use regularly. After several minutes, Firefox gives up trying, and becomes responsive again. If I click the same link, I get the same result. If I immediately try the same link in IE, it responds immediately without error. Back to Firefox - same non-response. I have done everything suggested on this site including reinstalling Firefox without any addons. I am really frustrated.