Add-ons

FlashGot Mass Downloader by Giorgio Maone

Download all the links, movies and audio clips of a page at the maximum speed with a single click, using the most popular, lightweight and reliable external download managers.

Element Hiding Helper for Adblock Plus by Felix Dahlke

Fight the text ads! Element Hiding Helper is a companion extension for Adblock Plus meant to make creating element hiding rules easier.

UnMHT by arai_a

UnMHT allows you to view MHT (MHTML) web archive format files, and save complete web pages, including text and graphics, into a single MHT file in Firefox/SeaMonkey.

VKontakte.ru Downloader (music/videos/photos @ VK) by Sergey Kolosov

Download music, videos and photos from VK.com / vkontakte.ru. One-click download, natural filenames, displaying file size and bitrate for music, downloading HD video, downloading HQ photos. No spam, no usage of your account, no spyware.

Linkification by y5

Converts text links into genuine, clickable links...

Scriptish by Erik Vold, Nils Maier, others

The greatest user script engine on the Internet (a fork of Greasemonkey).

Collector's Note Вместо Greasemonkey.

AutoPager by Wind Li

AutoPager automatically loads next pages when you reach the end of a page. It works on a ton of sites,Google,Yahoo..
It works well with most other add-ons adblock plus, WOT and most of the greasemonkey scripts.
You can also try AutoPagerLite.

Charset Switcher by yuoo2k

Supports to customize the Default Character Encoding for each sites.

Restartless Restart by Erik Vold

This 15KB restartless add-on will add a "File" -> "Restart" menu item and a ctrl/cmd + alt + r hotkey to restart Firefox or Seamonkey.

InlineDisposition by Kai Liu

InlineDisposition changes the disposition of Content-Disposition response headers from attachment to inline; this prevents servers from forcing the browser to save a file and allows that file to be viewed in the browser, if the browser supports it.

Edit Bookmark Plus by Kashif Iqbal Khan

Resize 'Add Bookmark' Popup / 'Edit This Bookmark' Popup, fixes tree selection bug, option to disable popup auto close & Update Url and/or Name of a bookmark with the Url/Title of current page.

Replacement of OpenBook addon