United States English Spellchecker for Firefox, Thunderbird and SeaMonkey by Kevin Atkinson and Geoff Kuenning.
To enable, right-click in a multi-line text box, select "Languages", then "English (United States)".
Check4Change (aka C4C) is a simple extension that allows you to select a part of a web-page, and get notified when it changes.
Integrate your Google Calendar with Firefox in a simple way.
No need extra login!!
Enables desktop notifications like in Chrome (e.g. Gmail, imo.im) and, if the site doesn't support them, it can notify new messages or updates detecting changes of the title (e.g. Hotmail, Yahoo, Facebook, Twitter). Even if the browser is minimized!
Make sure your tabs stay visible all the time.
This Add-on allows you to download every track from Soundcloud and in addition it gives you recommendations! After installing this Add-on you will have a new Download button at every track.
Bring back your personal and powerful Firefox Button!
This extension provides advanced configuration for your browser. It allows you to easily change many additional options, which are not displayed in the Firefox Options dialog.
Adds icons to your Firefox menus. Choose from the built-in icon sets or import your own.