In case you didn't already know, Firefox is a web browser that can be used to browse the Internet instead of Microsoft's Internet Explorer. I have been using the current version, which is Firefox 2 up until today, when I discovered Firefox 3 Beta. I downloaded and installed the Mozilla Firefox Beta 4 version on windows XP and here is what it looks like on the first load:
Of course the improvements are security, speed, etc. One tangible new feature is the new bookmark tagging ability. When you bookmark a page you can also add a "tag" to it to make organizing and searching for it later easier. Here is an example where I bookmark the Ubuntu Hardy Heron release schedule.
There is also the new location bar features. You can type in a page title, tag, or address in the location bar and it will search through your history and bookmarks and display a list of results. I grabbed a quick screenshot of it here:
You can read the actual Release Notes here. There are known issues. And of course, it is currently for testing purposes only.
Update: 13 Mar 4:30PM EST I performed an Acid3 test on the default install and here are the results: 67/100.
I think Firefox 2 scores at about 52/100.