I am seeking add'ons / application tools for FF to support my online researching. On my windows system I am using to help me determine, which websites might be useful by getting a snap shot of site traffic / page rank etc.

I am seeking something similar for my Mac, but so far havent been very successful.

Also, wondering where do you get most of your Mac add'ons / applications. For my windows system, I am using "download.com" and similar locations. But these do have not much useful stuff for Mac systems, and if anything most often very old versions...