Places is expected to replace the decade-old bookmark system with a new data-storage layer that will eventually also provide support for browser history, as well. The general idea behind places is to make it easier for users to both access and create bookmarks.
Also included in the Alpha 5 of Firefox 3 is a new crash-reporting system. Breakpad, formerly known as Airbag, is based on technology originally developed by Google.
With this release, Mozilla is also attempting to plug a particularly nasty problem that it has had in recent months with its Password Manager. Alpha 5 has a rewritten Password Manager that is an attempt to deal with a number of legacy issues that plague its use.
The release of Alpha 5 is a bit later than the original Mozilla plan had called for. The Alpha 4 release came out at the end of April, with Mozilla planning to release new versions every 30 days until July
The final Firefox 3 release is expected before the end of the year.