For Firebug 2.0 we had an
open beta phase of several months and provide alpha releases almost every week (just follow
blog.getfirebug.com), but unfortunately we didn't get any feedback about performance problems before the final release.
Constructive critique is always welcome. So if you want to help to avoid such problems in the future, please try out our alpha and beta releases and let us know when you see any problems.
Sebastian