Firefox Extensions

Extensions for Firefox are awesome. They're part of what makes Firefox great. Here are some of the best that I have found:

• Tab Mix Plus - Includes a ton of options and settings for how tabs and tabbed browsing operate. This is definitely better than the previous best extension for tabs, Tabbrowser Preferences.
• Google Browser Sync - Allows you to tie certain browser-specific user information, e.g., cookies, history, bookmarks, saved passwords, and sessions, to your Google Account. You can then sync any (Firefox) browser on any machine using your Google login. Thus, you can maintain the exact same list of bookmarks (and their folder structure) with very little effort. I love this one (although, I admit, all I use it for is the bookmarks). Think of it as logging in to your browser the same way you log into a specific computer - all your preferences come with you no matter what machine you're using.
• Image Toolbar - This extension gives you an IE style image toolbar when you hover over an image. The settings are fairly customizable. This one is quite handy.
• Download Manager Tweak - Gives you options such as loading the Download Manager in the sidebar or in another tab. Very nice if you do a lot of downloading since the standard Download Manager is so annoying.
• All-In-One Sidebar - While I don't find this one all that useful, I can see how it would be wonderful to anyone who uses the sidebar for more than one thing. I really only use the sidebar for bookmarks, but this extension allows you to change the content of the sidebar (between, for example, bookmarks, history, download manager, extensions window, page properties, etc.) simply by clicking one of the small icons it places next to the sidebar. Apparently, this mimics Opera's sidebar quite a bit.

If you know of any other really good ones, let me know.