Greasemonkey is a Firefox extension that allows you to write quick ‘n’ dirty Javascript scripts that execute on certain pages, allowing you to modify their behaviour. Here are some of the user scripts I’ve written.

To install, make sure you have Greasemonkey installed; then, simply right click the links and click “install user script”.

• PHP Code Whitener. Sets the background of PHP code displays on vBulletin forums to white, useful if the default colour scheme makes reading the syntax-highlighted code difficult.
• Nice Punctuation. In textareas, replaces regular punctuation with their typographic equivalent―three dashes becomes an em-dash, double quotes get converted to left and right quotes appropriately, etc.
• IMDb External Sites. Adds links to other sites (such as Criticker and Wikipedia) about the movie you’re currently viewing on IMDb.