• Live editing of CSS and (x)HTML
• CSS, RSS, and (x)HTML validation
• Resizing and hiding images
• Displaying element information (CSS attributes, parameters, topography, containers, etc.
• And tons more…

And since I'm talking about Firefox extensions, I might as well mention a few other of my favorites…

• IEtab – Never click on the "blue e" again! Keep Internet Exploiter, Exploder hidden on your system and for those few site that need it (Micro$oft Update, pages w/ activeX controls) view IE inside of Firefox. (Note: use this extension with care as it still has all the security problems IE does)
• Adblock or Adblock Plus – Get rid of popups, in-page ads, undesireable images, flash animation, iframes, and just about any other type of embeded media. Make sure you use this in conjunction with Adblock Filterset.G Updater. This other handy extension imports a whole list of filters (including several using regular expressions) to automatically block most unwanted ads.
• Remove it Permanently – this extension removes ads and media like Adblock, but it does a whole more. It can also remove text! Just select something, right-click, selete RIP and never see it again. This comes in handy when site are content w/ just displaying an ad, but they have to put ADVERTISEMENT surrounding it.
• A mouse gestures extension – there are serveral out there, but get one, because it speeds up browsing a whole lot!

Do you have any extensions you can't live without? Leave a comment and let me know about them. I used to browse through the whole list periodically, but its gotten too big now, and there are more sites that have them than just addons.mozilla.org.

Related posts:

• 100,000,000 Firefox downloads!
• Coming to you live from Linux
• Thank goodness for Windows security holes

Yeah, Firefox! The official time was was Oct 19 2005 1:13:40pm EST. Join the celebration at the newly restored spreadfirefox.com!

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• Firefox extensions