Extensions by Weekly Downloads

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Provider for Google Calendar

Allows bidirectional access to Google Calendar

Rated 4 out of 5 stars (1,027)
11,238 weekly downloads

Xmarks Sync

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!

Rated 4 out of 5 stars (2,535)
10,344 weekly downloads

Youtube MP3 Podcaster

Self contained add-on for downloading youtube videos to mp3 for easy listening on podcasting gadgets like a Zune or iPod

Rated 4 out of 5 stars (213)
10,007 weekly downloads

JavaScript Debugger

As of Firefox 33, Venkman *no longer works*, as the APIs which it needs have been removed.

Venkman is the code name for Mozilla's JavaScript Debugger. Venkman aimed to provide a powerful JavaScript debugging environment for Mozilla based browsers.

Rated 4 out of 5 stars (50)
9,324 weekly downloads

Session Manager No Restart

Session Manager saves and restores the state of all or some windows - either when you want it or automatically at startup and after crashes. It can also automatically save the state of open windows individually.

Rated 5 out of 5 stars (447)
9,016 weekly downloads

Fire IE (FireIE, Enhanced IE)

Embeds Internet Explorer(IE) to use the powerful Firefox add-ons.
Not only an enhanced IE Tab, but also an enhanced Internet Explorer with Adblock Plus and FireGestures support.
Switch to the IE engine in one click and dismiss your IE.

Rated 4 out of 5 stars (159)
8,870 weekly downloads

MP4 YouTube Downloader

This simple add-on allows you to download MP4 (iPod-compatible) videos from YouTube, Dailymotion, and Vimeo.

Rated 4 out of 5 stars (59)
8,670 weekly downloads

ColorZilla

Advanced Eyedropper, Color Picker, Gradient Generator and other colorful goodies...

Rated 5 out of 5 stars (306)
8,454 weekly downloads

LookOut

LookOut is a plugin which allows Thunderbird to interface with Microsoft's mail tools by decoding metadata and attachments encapsulated/embedded in a TNEF encoded attachment (aka winmail.dat).

Rated 4 out of 5 stars (147)
7,764 weekly downloads

Torrent Tornado

A Torrent Client for Firefox and SeaMonkey, runs everywhere, created in pure JavaScript without binary software!

Rated 4 out of 5 stars (64)
7,578 weekly downloads

Enigmail Featured

OpenPGP message encryption and authentication for Thunderbird and SeaMonkey.

Rated 4 out of 5 stars (183)
7,040 weekly downloads

Live HTTP Headers

View HTTP headers of a page and while browsing.

Rated 4 out of 5 stars (164)
6,654 weekly downloads

Screengrab (fix version)

Screengrab! saves webpages as images.
0.98 released!
New features: upload to internet

Rated 5 out of 5 stars (276)
6,540 weekly downloads

AntiGameOrigin v6 No Restart

AntiGameOrigin - the other OGame experience for all communities.

Rated 5 out of 5 stars (3)
6,505 weekly downloads

AutoProxy

Are you concerned about your privacy? Or, are you blocked from some websites by a firewall? And, are you arming yourself with a proxy? In that case, AutoProxy is designed for you! A tool to help you use your proxy automatically & efficiently.

Rated 4 out of 5 stars (416)
6,415 weekly downloads

Easiest YouTube Video Downloader No Restart

This Addon simply adds a dropdown button that lets you download YouTube Videos in various Formats. Download YouTube Videos in FLV, 3GP, MP3, MP4, 720p, 1080p in a single click.

Rated 3 out of 5 stars (30)
6,290 weekly downloads

Thumbnail Zoom Plus

Shows full image when you hover over a thumbnail. Works with Amazon, Baidu Images, Bing Images, Facebook, Flickr, Google+, Google Images, IMDb, LinkedIn, Netflix, Pinterest, Reddit, Twitter, Yandex, YouTube, Wikipedia, Yahoo Images, & many more.

Rated 4 out of 5 stars (313)
6,209 weekly downloads

Facebook Messenger No Restart

Facebook Messenger lets you bring a Facebook Messenger right into your browser to chat with your friends.

Rated 5 out of 5 stars (29)
6,181 weekly downloads

Google search link fix No Restart

This extension prevents Google and Yandex search pages from modifying search result links when you click them. This is useful when copying links but it also helps privacy by preventing the search engines from recording your clicks.

Rated 5 out of 5 stars (118)
6,174 weekly downloads

Theme Font & Size Changer No Restart

Theme Font & Size Changer lets you change the global font size and font family used for the user interface in Firefox. Design your browser with your favorite font.

Rated 5 out of 5 stars (164)
5,979 weekly downloads