I have Firefox set as my default browser, when i go on Facebook and try to accept friends requests, post comments etc it doesnt work for some reason

I click "Accept" and nothing happens, it just says Done at the bottom of the page (which it does when it fully loads any other page), ive tried doing this on internet explorer and it doesnt work on there either. Is there some kind of plug-in i need? Anything i can do to stop this happening?
Any help appreciated.
Thanks.