I'm pleased that you've got that bit sorted.
If you still experience problems with Firefox running slowly, try resetting it. (These instructions assume that you've got 'File', 'Edit', 'View', etc visible across the top of your screen. If not, right-click up there and put a tick next to 'Menu Bar'):
Go to Tools > Add-on and click on 'Extensions'
Note down the names of any extensions you want to keep (because you're about to remove them).
Close the tab.
Then go to Help > Troubleshooting Information and click on 'Refresh Firefox'. (Don't worry. You won't lose your bookmarks!)
Return to 'Extensions'. Search for and reinstall those you still need.