Greasemonkey is a Mozilla Firefox extension which facilitates page customization by running user scripts after the page has loaded. This is similar to using custom CSS, but allows for far greater control, such as adding or removing elements and matching with regular expressions.

AdBlock Filter:
Generic regex-based ad-blocking filter, a poor man's AdBlock (more of a POC/template than anything else)
EasyNews Enhancer:
Enhance various aspects of EasyNews searches by highlighting AutoUnRAR & AutoPAR links and today's posts in the global search & beta indexes and optimized for speed. Colorization has been delegated to the browser (<profile>/chrome/userContent.css, Stylish, etc.), see easy.css for EasyNews-related rules and customize as necessary.
EasyNews Search Filter:
Filter and enhance EasyNews search results
 
Note: Deprecated in favor of EasyNews Enhancer
 
Prefs:
   .colorize: colorize links (boolean; default: true)
   .AutoUnRAR: color for 'AutoUnRAR' links (string; default: #ff000)
   .color1-25: 1-10 defaults, 11-25 empty (string; #hexcolor|regexp/string)
      1: #4682b4|\.(nfo|txt|sfv|crc|cue)$
      2: #20b2aa|\.par2?$
      3: #6b8e23|\.nzb$
      4: #9932cc|\.(jpe?g|png|gif|bmp)$
      5: #9370db|\.(mpe?g|avi|wmf|mov|rm)$
      6: #c71585|\.(mp3|wav|wma|ra)$
      7: #8b008b|\.(m3u|pls|ram|b4s|asx)$
      8: #8b0000|\.(tgz|gz|bz2|r(ar|[0-9]{2}))$
      9: #daa520|\.zip$
      10: #32cd32|\.(exe|com|pif|bat|sh|bin)$
Focus First Input:
Focus the first viewable input on a page (ltr, ttb)
Geocities Frame Remover:
Remove the sponsored links frame from Geocities pages
Google Groups Filter:
Hide google groups search results by group name
 
Prefs:
   .exclude: regular expression (string; default: \.((announce|linux\.advocacy|ports)$|cvs))
Google Heading Adjuster:
Bummed about Groups being relegated to the more » menu? Use this to customize Google's search headings.
IGN Interstitial Skip:
Automatically bypass interstitial ads on IGN-owned sites
No Right Click Disabler:
Override most right click disablers
SF Auto-Mirror Links:
Transform Sourceforge download links to a preferred mirror
 
Prefs:
   .maxLinks: don't process pages tha contain more than maxLinks links (int; default: 1500; 0 to disable)
   .mirror: selected mirror (string; default: randomly chosen on first run)
TV.com Interstitial Skip:
Automatically bypass interstitial ads on TV.com
URL As Link Title:
Set the URL as the link title
WinSite.com Interstitial Skip:
Remove the interstitial ad handler for download links
vBulletin Tooltip Remover:
Remove vBulletin table tooltips
Yahoo TV Listings Enhancer:
Enhances Yahoo TV listings (tv.yahoo.com); program info displayed in a small layer

Related: userscripts.org, Greasemonkey compiler.