If you’re a web developer and you don’t have this extension installed, then you deserve a slap about the face. Firebug has so many useful features I could rant on for ages, but here are the highlights:
- Inspect and edit HTML and CSS inline
- DOM Explorer
- Monitoring and debugging of requests and responses using XMLHTTPRequest
- File sizes and timings display
I really can’t say enough good things about this extension, and this latest version is a massive improvement over previous releases.
UPDATE: check out this interesting article exploring just some of Firebug’s features.