Since i have tried beta 2 of Firefox 3, i tried to download the beta 3 and tested it on my Slackware box. First, i have to move my .mozilla directory to another name so that my old configuration and settings will be safe. Next, i extract the Firefox 3 beta 3 package and call the package which will execute the Firefox and launch it.
According to the Release notes, it has fixed more than 1300 changes, but we may not see most of them. As far as i see, the security settings, mostly related to SSL and forgery websites protection are functioning as stated, so it's a good thing by the Mozilla team. I do hope they will polish the UI, since in it's default installation, it's so plain.
About the memory consumption, they do have fixed some of the memory leaks and it does a little bit lower on memory consumption, so it's a good sign to have a better Firefox in the future. It's only a small testing on Beta 3, not a detailed testing, so you might not get full review on this blog. I believe others will post up a better posting about Firefox 3 Beta 3.
In my opinion, Beta 3 is quite stable and Mozilla team has done a great job to make it possible from the last beta. I hope they will have a solid RC release and finally a final version for public. We are all waiting for that