These two arent fun but they’re help keep you safe.
Adblock Plus and Noscript.
Download Statusbar makes the downloading interface a lot nicer too.
I should stress that you shouldn’t install Filterset.g if you get Adblock Plus. Adblock Plus updates itself.
Remove It Permanently allows you to just cut elements out of a webpage in a persistent fashion. You can cut things out of that page, all similar pages, and even all pages in that domain. Very useful.
Well, it’s not an extension, but…
This is something I did to my firefox at home, as well as here at work.
- In the address bar, type in “about:config” (no quotes please!)
It might give you a warning to not mess with it unless you know what you’re doing. Say okay to that.
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In the filter bar (which is basically like a search), put in “network.http.pipelining” (again, no quotes)
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Set network.http.pipelining to “true” if it isn’t by double-clicking it.
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Double-click network.http.pipelining.maxrequests to make a new window pop up. This displayed number is basically (AFAIK) how many connections your computer opens to a site when you go there. Think of it as drinking a soda through more straws. More numbers, faster page load times. Don’t make it too high, though. I keep mine at home around 10 IIRC.
I also set network.http.proxy.pipelining to “true” but I’m not sure if it did anything. Didn’t seem to hurt anything anyway.
This didn’t hurt my firefox/computer at all, but as always, just gotta say the disclaimer to mess with things in that configuration screen at your own risk. 
Hmm. Looks like something updated when I wasn’t paying attention. Well, you live, you learn. Deskcut, though, is a right-click send to desktop shortcut thing. My dad loves it.