Mozilla has officially released the Firefox 2.0 (Bon Echo) Alpha. Due out later this year, Firefox 2.0 will include a handful of improvements and new features. These changes include a new storage system for bookmarks and history. The Places window is one of the biggest changes for the end user. This window allows the user to search their history, bookmarks, and RSS subscriptions by keywords. There are also a few minor tweaks to the UI, such as Xs on inactive tabs for easy closing (for those who do not like this approach an extension called Tab No X reverses the close buttons on tabs or you can use the Tab Mix Plus developer extension).
If you plan on installing this version of Firefox be forewarned this is alpha software so you will face some crashes while using it and all of the features are not fully complete (a list of the known issues is here. In addition, many extensions will not work. The best way to go about playing around with it then is to use a portable version of the build. This will allow you to use a separate profile from your original installation of Firefox. Secondly, if you want to try out extensions that will not install under Bon Echo grab a copy of the Nightly Tester Tools extension. This allowed me to easily install and run the excellent Web Developer extension, for example. There is no guarantee that an extension will work correctly, but most of the times they will.