Comment 2 for bug 369552

Many bad Firefox behaviors are in fact caused by one of the many third-party 'themes', 'extensions' and 'plugins'. These will go away with a new profile - that is, when Firefox is restored to default settings and without any extensions and themes.
Please follow these instructions and try that site with a new profile:
https://wiki.ubuntu.com/MozillaTeam/Bugs?action=show&redirect=DebuggingFirefox#Try%20with%20a%20new%20profile