extension

ImTranslator provides additional multilingual capabilities to Internet Explorer and Firefox for more efficient communication in foreign languages.

「HTML のソースを見ながら、属性値を直接編集できる」FireBugすげぇ

FoxyVoice is a Firefox extension that provides text-to-speech functionality using Microsoft Win32 Speech API (SAPI). With FoxyVoice you can listen to the page being read; or browse on one page and listen to another page being read for higher degree of sen

This is (the only?) thing I miss from IE. Thankfully, this Firefox extension adds the capability.

Quoted: Allows you to open any file from the internet into the OS assigned program. This is similar to IE's 'Open' or 'Run' file download functionality.

createUnique, nsIFileOutputStream

Quoted: バイナリファイルを書き込む
例として、PNG データをファイルに書き込むサンプルです。

Blog post from Facebook confirming the new News Feed behavior.

Quoted: As part of our ongoing improvements to News Feed, we recently made it possible for users to see stories from applications they have not added.
...
Use feed.publishTemplatizedAction and register your story templates with us. Only stories with registered templates will be visible to users who have not added your application. (Note: We recommend using feed.publishTemplatizedAction even if you are not registering the template because feed.publishActionOfUser will eventually be deprecated.)

OK, so this pretty much rules. I have no idea why this isn't simply part of the core DOM inspector package.

Quoted: Adds an entry to the context menu to open the DOM Inspector on the selected element.

Video Downloader 2.0 and VideoDownloader 1.O Firefox Extension allows you to download videos (to your computer)