Rated 5 out of 5 stars
Absolutely love this addon. It's one of the first things I install when I reinstall FF.
For me it does exactly what I want it to: allows me to quickly change my css in the browser in real time before I save that file for upload later (unlike firebug). Changes are persistent until I close the sidebar *AND* reload the page (unlike WDT).
The simplicity is one of the things I love about it. I don't need auto completion, highlighting or anything else really-if I need any other features I use Coda.
I don't have any stability issues. I think it's pretty perfect.