I have a problem when i try to install a new extension and after restarting the browser it still gives me the need to restart msg and the extension is not working ? how can i fix this ?

What browser, Os , and extension.?

Try this: first make sure Firefox is closed, then go into your Firefox profile folder and delete these files:

extensions.ini
extensions.cache
extensions.rdf

Now see if your problem is still occuring.

Thanks it worked