SeaMonkey Extensions compatible with version 2.2 for any regular user. If you are missing any, then it is not compatible. Of course, this is not exhaustive list, so visit frequently for any inclusion.
NewsFox is an efficient 3-pane(email) style Atom/RSS feed reader.
Extends the function of the drag-and-drop mouse gesture so that it can be used to load URLs, do a web search of selected text on a page, or save an image on a page. The successor to Super DragAndGo.
Adds Tools menu item to check Add-ons for updates. Includes toolbar icon.
Allows for customization of the folder pane. Accounts can be rearranged and the startup folder can be chosen.
This extension prevents websites from interfering with your copy and paste actions.
Note: The same functionality is now built into Firefox, you can just change the dom.event.clipboardevents.enabled preference manually.
Adds extension options dialogs to the Tools or Titlebar menu and includes toolbar icon.
Persistent sticky notes for Thunderbird associated to mails.
This is a port to Thunderbird >= 3 and Seamonkey >= 2 based on XNote 2.1.0 ( https://addons.mozilla.org/en-US/thunderbird/addon/3093 ) with bugfixes and additional features.
A no-clutter image viewer for Firefox that allows you to zoom, rotate and display images/videos against a custom background. ImageTweak is a must-have addon for any photographer or photography-loving user.
add icons to buttons/menus/anywhere (CuteMenus - Crystal SVG not required)