Firefox plugins:
Abduction! can take screencaps of entire pages, not just what's in the window at the moment. Saves in PNG format (at least, on my machine it does) so just select what of the page you want to save, and save it. I love it. Edit: This doesn't work with Firefox 3.6.3, unfortunately. I'm looking for a replacement, but it's not my highest priority. Last checked: April 22 2010. Hopefully they'll update it soon.
AdBlock Plus, in case anyone actually doesn't already have this, gets rid of ads on pages. Including that godawful "I'm waiting for you, my lord!" one with the blond lady who looks more like she's trying to do a softcore porn ad than any sort of MMO strategy game ad. :|
Image Zoom lets you zoom in to make a small image bigger, or out to let you shrink an image. I'm not talking about zooming the whole page, I mean just resizing the one image. It's something I find I use often enough when browsing forums or wherever, and someone puts in a freaking huge image that just... breaks the page. Or you're on deviantArt and there's an image posted that's too small to appreciate when it's just a thumbnail or in small-view, but way too freaking huge to fit on the screen in full-view because the poster hasn't a clue what "DPI" means, or else your monitor's just small. Stuff like that.
Lazarus lets you resurrect your tags. You know how sometimes you press Submit on your tag, and then LJ decides not to post it anyway? Like either because the site went down once again, or because your post-session timed out, or whatever the reason is, and then you're usually left going OMG NO MY TAG I WORKED SO HARD ON AAAACK!!! and stuff.... well, it saves your posts so you don't have to flip out. (Actually, I found that if I took too long to write my TL;DR tags, and LJ gave me the "Invalid form submission" page, all I had to do was press BACK to go back to the post page, click "Reply" or whatever it was I'd clicked to bring up the post field, and then select and copy it all. THEN hit refresh, and try it again. CACHES ARE WONDERFUL THINGS. ♥ But this little thing's a lot more reliable, and far easier. So uh, yeah. I'm totally listing it here.)
LiveJournal Addons is sorta like having a Paid account and then a bit. Only, without having to pay. And without the extra icon storage. Formatting tools for writing/editing comments, helping you track your f-list and comments, expanding threads, expanding LJ-cuts and... and you know you want this. Even if you have a Paid. Get it. Also, its help page on LJ is in Russian, but Google Translate is a handy thing.
As evidenced. I'm still fiddling with this add-on myself, but so far, the comment expanders and LJ-cut expanders are more than enough reason for me to always have it installed. ♥
LJ Login has got to be one of my favorite Firefox additions of all time, now that I've started using it. It makes it so easy to switch between LJ accounts... you just put in your login info in it, and then all you need to do is click and select which one you want to switch to, and it'll take care of the rest. I'd been using different browsers for each of my different rp accounts, to make it easier on me, and this is... yeah. I love it muchly. Note: Firefox has to have the login and password saved too, for that login to show up on its list. Just go to LJ's front page and save it from there, and your troubles should be over. :)
Stylish lets you override a page's CSS with your own. Sound like much effort? Let me get you started with
some code I did for it -- you might find it useful. :)
Text Area Resizer & Mover does just what it says: lets you resize text-entry areas. As TL;DR tags are my friends, this is a blessing. omg yes. (Note: you'll want to configure it after it's installed. I set it up so that I have to right-click to resize text areas... otherwise, it acts pretty funny.)
Suggestions for further additions are welcome! I'm mostly looking for "most useful add-ons" and things a person can find helpful on a daily or near-daily basis.... :)
Edit: Please do look in the comments for more add-ons!