For those who don't already know, the JavaScript console is one of the greatest tools built in to Firefox. It makes finding JavaScript errors a breeze, and can be a life-saver for extension developers. Unfortunately, the console has become rather bloated in Firefox 1.5. Not only do JavaScript errors appear, but now CSS errors (which are way more likely to appear on various websites) are also logged. This results in a terribly cluttered console, making it hard to find what you're looking for.
Thankfully, I was recently pointed to the Console2 extension (which only works in Firefox 1.5). This extension makes it possible to filter out CSS errors, in addition to a number of other great features. It smartly renames JavaScript Console to Error Console (CSS != JavaScript), and is an excellent light-weight solution to the bloat added in 1.5.