While Greasemonkey, the popular extension for changing the way websites display, might not be currently available via the Firefox 3 addons manager or the Mozilla addons website, you can indeed install a working version from the developer's site. We installed the greasemonkey-0.8.20080609.0.xpi into Firefox 3 RC2 on Mac OS 10.5, and our scripts worked like a charm.

In case you're new to the Greasemonkey realm, here are three scripts to get you going:

• Gmail 2.0 Multiple HTML Signatures - allows you to maintain a set of HTML signatures for Gmail that are automatically changed when you select different "From" addresses in your compose mail window. Alternatively, you could use a bookmarklet.
• Digg Add Mirrors - adds links to Coral Cache, Duggmirror, Duggback, and Google Cache to Digg stories.
• Image Host Redirector - redirects image links directly to image instead of intermediate image host page.

[via gHacks]