Lifehacker just posted a bit about a new Firefox extension that changes how Craigslist works. There are a mess of extensions for Firefox that do stuff like this. (My personal favorite blocks annoying flash and banner ads.)

Craigslist Image Preview adds a thumbnail of the image(s) within a listing on Craigslist without requiring you to click through to the actual page. Since most Craigslist ads live or die by the included image of what’s actually being sold, this extension saves a ton of time and is a must-have for any Craigslist shopper.

In my mind, this fits in the same category as RSS feeds, podcasts and Tivo. Users are gaining the ability to absorb media at their own pace and in the format they prefer.

What made it possible? Open standards, like HTML and RSS, and open systems like Firefox’s add-on framework. This would never have happened on a proprietary system. You can’t do this to Microsoft Office.

Craigslist just got more useful, and it didn’t cost Craig, or you, a dime.