Hi, in the time I helped people in the Support Forum at Mozilla Hispano (in Spanish) I’ve seen a couple of serious issues in Firefox whose solutions are very simple.
1. Facebook / Youtube / GMail / a popular page doesn’t load correctly
Almost all the times is a problem related with ‘cookies’. To solve this, go to History -> Clear Recent History. There choose in Range: Everything and in Details select all options except the two first ones.
Then, you just need to click in Clean Now. Depending of the quantity of data you have stored, this operation will delay some seconds and then the window will close automatically.
2. I can’t change my Home Page / remove a Search Engine / my Firefox behaves weird
Most of the time these troubles are caused by malicious programs (Malware) that are difficult to remove. Luckily in Mozilla designed an option called Restart Firefox.
In order to use this, you should go to Help -> Troubleshooting Information. There choose the button Restart Firefox. A confirmation window will appears, and then you need to wait some minutes while Firefox restores everything (well, almost everything because your history will be saved).
Just a note: if you have addons you should annotate them before, because this option will delete them. As usual, the extensions are in Tools -> Addons.
EXTRA: I don’t have an icon o a button in the toolbar.
The solution is simple: go to View -> Toolbars -> Customize. In the new window will appear all the available icons. You just need to drag the lost one and drop it in the place you like ¡and that’s all!
¿You couldn’t find your trouble? The best place where you could get more help is Mozilla Support.