|Can be tricky because Norton might have removed stacks of registry entries. It's about crazy that Norton does not provide an undo.|
Did you try System Restore as mentioned in #1?
Re-installing your browser might also fix it.
You could try this but I cannot vouch for it:-
For the future get yourself a copy of ERUNT. Use this to backup your registry when you are about to take a risk, such as using a registry cleaner. It's worth backing up your registry from time to time anyway (when things are going well).
some other bloke...