Try redownloading Firefox. Does this happen with Firefox 13? Any other earlier Firefox version? If it doesnt work, give me the add-ons you want to install and maybe i can provide you with the direct link or you can search it with Google perhaps.

Thank you for your response, but I tried again just now out of curiosity without uninstalling and re-downloading, and it worked. So I guess I was just having connection problems or something instead of it being a problem with Firefox itself. This will probably sound pretty stupid, but do you know if there's something I'm supposed to do to mark my problem as being solved? Am I just supposed to click on the link next to your post, or is there anything else I'm supposed to do? Thanks.