Essential Firefox addons
to make screenshots and save to files or to clipboard.
to allow you use mouse gesture to control Firefox.
if you would like to block ads.
Optional addons for specific users
to convert webpages to ebooks.
to switch user agents Firefox shows to websites.
All Downloader Professional https://addons.mozilla.org/en-US/firefox/addon/all-downloader-professional/
if you download frequently.
FoxyProxy – Proxy manager.
FoxyProxy is an advanced proxy management tool that completely replaces Firefox’s limited proxying capabilities. It offers more features than SwitchProxy, ProxyButton, QuickProxy, xyzproxy, ProxyTex, TorButton, etc.
Tab Mix Plus – Improve the Tabs.
Tab Mix Plus enhances Firefox’s tab browsing capabilities. It add to Firefox features like duplicating tabs, controlling tab focus, tab clicking options, undo closed tabs and windows, plus much more.
Previously suggested addons (may be already outdated)
FireGestures – Control Firefox with mouse gestures/
A customizable mouse gestures extension which enables to execute various commands and user scripts with five types of gestures.
Flashblock – Block flash/
Never be annoyed by a Flash animation again! Blocks Flash so it won’t get in your way.
Screengrab (fix version) – Screenshot tool for webpages.
Screengrab! saves entire web pages as images. It will capture what you can see in the window, the entire page, just a selection, a particular frame.
Downthemall! – Download manager.
A great download manager/accelerator built inside Firefox. Be in full control over your downloads, dedicated speed and number of parallel connections at any time.