Firefox: Mozilla's out with the 1.0 of its Weave project, and it delivers on what it first promised — quiet but complete syncing of bookmarks, passwords, preferences, history and even open tabs. It also heralds the coming of a really cool mobile experience.
If Weave synced your currently installed add-ons, you'd be up and running after a fresh Firefox installation in two minutes. As it is, Weave is still a very efficient and lightweight sync of your core Firefox experience, allowing you to maintain multiple Firefox installations across computers and operating systems. Xmarks does the same thing, and across other browsers too, but Weave doesn't offer site "discovery" services or other value-added stuff — just a way to automatically connect your Firefox browsers, and even browsing sessions.
That syncing of open tabs is where Firefox Mobile, just out in a third release candidate, will really shine. As Jay Sullivan told us, the idea is that the minute you step away from your desktop or laptop and wake your phone up, Firefox Mobile will pick up on the tabs you had open while you were sitting down.
Weave syncs through Mozilla's servers. If you'd rather sync up your passwords and bookmarks to your own hardware or cloud space, Mozilla offers instructions on setting up your own server.
Weave 1.0 is a free download, works wherever Firefox 3.5 or higher (or Firefox Mobile) does.