I'm not having any problems so far, so it might be a problem with your computer, or perhaps something went wrong when you installed the update. Or there could be a conflict with your extensions, or you might just have too many extensions. There are several possibilities. Anyway, rolling back to a previous version is not recommended, and I've read that the only stable version other than 5 is 3.6.18. However, you can find all versions at ftp://ftp.mozilla.org/pub/mozilla.org/firefox/releases/. If you want to install an older version, another user named jscher2000 said: "First, I recommend backing up your Firefox settings in case something goes wrong. See Backing up your information. (You can copy your entire Firefox profile folder somewhere outside of the Mozilla folder.) Next, download and save Firefox 3.6 to your desktop for future installation. ... Close Firefox 5. You could install Firefox 3.6 over it (many have reported success) or you could uninstall Firefox first. If you uninstall, do not remove your personal data and settings, just the program." He was referring specifically to 3.6, but his advice should work for any version, I think. Including FF4. But again, rolling back isn't recommended.