A collection of add-ons that I've found to be indispensible.
Blocks annoying video ads on YouTube, Facebook ads, banners and much more.
Adblock Plus blocks all annoying ads, and supports websites by not blocking unobtrusive ads by default (configurable).
Collector's Note Seriously unclutters and speeds up a webpage by weeding out the ads, so you can focus on the content.
Tab Mix Plus enhances Firefox's tab browsing capabilities. It includes such features as duplicating tabs, controlling tab focus, tab clicking options, undo closed tabs and windows, plus much more. It also includes a full-featured session manager.
Collector's Note You’ll wonder how how you lived without it.
Xmarks is the #1 bookmarking and open tab add-on. Keep your bookmarks, and open tabs backed up and synchronized across computers and browsers. Mobile phones with Premium access. Utilize LastPass to sync passwords!
Collector's Note Combined with Firefox Portable on a USB stick, it’s like I’ve never even left my desk.
Use PDF Download to do whatever you like with PDF files on the Web. Regain control and eliminate browser problems, view PDFs directly in Firefox as HTML, and use the all-new Web-to-PDF toolbar to save and share Web pages as high-quality PDF files.
Collector's Note A great tool for managing web-based PDF documents.
IE Tab - an extension from Taiwan, features: Embedding Internet Explorer in tabs of Mozilla/Firefox...
Collector's Note Indispensible: For sites that don't play well with anything but Internet Explorer, a single click of the icon switches your browser engine to IE for that single tab.
Notifier for gmail, yahoo, hotmail, aol and more webmails.
X-notifier(aka WebMail Notifier) checks your webmail accounts and notifies the number of unread emails...
Supports : gmail, yahoo, hotmail, POP3/IMAP, facebook, twitter and more
BBCodeXtra is an extension, compatible with Mozilla FireFox and Seamonkey, which adds to the context menu new commands to insert BBCode/Html/XHtml codes in an easy and fast way...
Collector's Note A great time-saver if you do a lot of forum/blog writing.