Syndic8's Jeff Barr half swicthed to Mozilla but misses Google and Alexa Toolbars.
The mozdev project Googlebar, provides a pretty good equivalent of the Google Toolbar functionality.
I use it since I switched to a Mac and am happy with it.
For Alexa I did not find anything: maybe the Googlebar team should enhance it to add Alexa's features.
PS: I initially wanted to add a comment on Jeff's weblog but he closed comments off. I'll try to Trackback it with this entry. This is the sad reality of spam coming to weblogs through comment spam.
Erik Benson's proposed Talkrnet proposal would be a good first step to solve this issue without blocking communication. Using social software to determine who's trusted to comment is a good ad-hoc practical first step. The next step will be a standardization of the interface to such a trust service: managing digital identity and trust and the next big problem to be solved.