I also use the extension called FLST(focus on last tab). This extension's purpose is just like it's name says, if you have say, five tabs open and you
are looking at the first tab then you go to the fifth tab, when you close the fifth tab Firefox will go to the fourth tab.
When you have FLST enabled when you close the fifth tab it will go to the previous tab you were looking at, back to the first
tab in this case.
The third extension I have installed is
FireFTP. Firefox isn't a FTP client, meaning it can't upload things to a ftp server, it can download things but not upload.
FireFTP allows you to have folder view and upload and download very easy.
The fourth extension I have installed is
Permit Cookies. I uncheck the "Allow sites to set cookies" in the options, then if I come to a site that I want to set cookies I
press alt-c and it puts that site in the cookies exception list. From then on that site will be able to set cookies until
you remove it from the list in the Firefox Tools > Options.