I just downloaded the RC3 Version of Firefox 2.0 (For Mac) and decided to try it out. So far I think it's an enormous improvement over 1.5. And It's still a fair bit ahead of IE7.
I will list a few of the things that I noticed about Firefox right away:
Firefox maintains a list of known or suspected Phishing web sites on your local computer, it will update this list every half an hour or so.
When you visit a website, it checks the address against this list and if it finds a match it warns you.
NO INFORMATION ABOUT THE WEBSITE YOU ARE VISITING (OR TRYING TO VISIT) IS TRANSMITTED TO ANYONE.
On IE7 however, every url you visit is transmitted to a server on the Internet (one of Microsoft's servers presumably) and your web browser waits for a reply from this server letting it know if it should warn you or not.
This method is much slower than the method Firefox uses (Because it has to wait on the servers reply before it can load the page), not to mention the fact that every web site you visit is transmitted to Microsoft (or other unknown third parties) this sounds like a very very bad idea to me.
How do we know what Microsoft is planning on doing with the enormous amount of data this process must collect. This is yet another example of Microsoft invading the privacy of it's users.
It's roughly analogous to the function that "Windows Genuine Advantage" performs only on a much much larger scale. I can tell you that I wont be using this feature of IE7 at all after learning how it works.
Conclusion: After using each new browser for a rather short time, it's very clear to me that Firefox 2.0 is still the superior choice for browsing the web. (In My Opinion) Internet Explorer v 7 is a big improvement over the previous version (IE6) and if you insist on using IE then I strongly recommend that you install it.
But it doesn't have any features that Firefox is missing that I can see, and there are serious privacy concerns surrounding the Anti-Phishing support in IE7. For me this (and spell checking) is enough to prevent IE7 from usurping Firefox as my default browser.