On Safari there's an option to reset the browser which deletes the history and removes all the cookies; I think that's called emptying out the catch. How do I do that on Firefox?
A couple of things should be set to do it, but you go into Preferences, then click Privacy.
After that, go to the Private Data section and click settings. After that, you can confirm or cancel. On the main dialog, click the Clear Now... to clear things just then or without the Ask me... checked, it will clear it everytime you quit.
if ur firefox totally messed up, do a "hard" reset
delete ur profile folder, this will solve almost all the problems, but u will lose bookmarks, password, extensions, themes. (u can back up your bookmarks and passwords before u do this)