Scriptify is a light weight extension for Firefox that provides a hassle-free way to convert any user script to a standalone add-on for Firefox.
Userscripts
Prevent Facebook, Google and Twitter from changing links posted on it with these handy userscripts. Scripts work on Google Chrome, Opera and Mozilla Firefox.
Get back old Twitter layout with Timeline on the left and account summary, trending topics, etc on the right on Google Chrome and Firefox
Soundcloud Super +2 is userscript that adds an option to download music from SoundCloud as an MP3 file. It works on Chrome, Firefox and Opera.
Get back the classic layout in new Google Reader with ‘Google Reader compact’ userscript. It works on Google Chrome, Firefox and Opera
Facebook Fixed Header is a userscript that keeps the Facebook navigation menu ‘fixed’ to the top of the screen, while the content scrolls under it.
Gmail Preview Pane Extend userscript removes the right-sidebar in Gmail and extends Preview Pane to the full width of the screen. It works on Chrome and Firefox.
Facebook Sidebar Chat Reversion is a userscript that brings back the old Facebook chat layout and functionality. It works on Google Chrome, Mozilla Firefox and Opera.
Google Light Navbar is a userscript for Google Chrome, Mozilla Firefox, and Opera that lets users customize the Google Navigation Bar color to anything they want
Disable the New York Times paywall on Google Chrome, Mozilla Firefox, Opera and Internet Explorer, to get unlimited articles access.