Greasemonkey is the handiest Firefox extension ever.
- ununderline: Convert all non-link underlined text to italics, so only links are underlined
- Linkify: Convert all text URLs to clickable links
- Livejournal userpic adder: shows LJ userpics when you mouse over a Username
- del.icio.us skin 2: different look for del.icio.us
- ALT tooltips: makes Firefox show an image’s alt attribute on mouseover when there is no title attribute
- Newsmasher: adds a floating link at the top of every page which brings up a floating iframe containing the del.icio.us posts for a URL, so you can read other people’s comments about it
- Friend of Print-Friendly: takes you directly to printer-friendly pages on a whole bunch of websites
- Expand Area: lets you drag the corner of a textarea to make it bigger (this one is a great example of how flexible and useful greasemonkey is)
- Check Range: lets you check a range of checkboxes by clicking one at the beginning and then shift-clicking one at the end of the range
- Salon Auto-Pass: bypasses the Salon daypass requirement
- Metafilter deleted posts: shows links to deleted posts on Metafilter
I’ve written a couple of user scripts already:
- SourcePlease: rewrite sourceforge download URLs to point directly to a file instead of their “Choose a mirror” page
- HTTP-Be-Gone: remove the example “http://” from form fields that expect a URL, so you don’t have to see “http://http://” after you paste
There’s another hundred or two user scripts available on the GreaseMonkey wiki — reading through the list there will give you an idea how great this thing is. I never really found user CSS that useful, but being able to fix webpages to work the way you like is incredibly handy.