I’m sure that all of Firefox fans are so eager to try the new beta 4 of Firefox 3. As it is still in beta version so it is not ready for daily browsing use. Other reason that you shouldn’t use it (yet) for daily use are a lot of themes, plug-ins and extensions of Firefox 2 will not compatible with Firefox 3 beta 4.
But I’m sure that your curiosity is getting high, right? Then you can try Firefox 3 Beta 4 Portable from PortableApps.com. The benefit of using the portable version is you don’t need to install it, you just run the auto extract package file to a directory, then click on the Firefox executable files and Firefox 3 beta 4 will run. Another good thing is, it will not interfere your existing Firefox 2 profiles.
Download Firefox 3 beta 4 portable here.