Firefox 11 now allows you to migrate history, bookmarks and cookies over from rival Chrome. Additionally, you can now sync extensions between your computers. File storage is now in IndexedDB and SPDY protocol support for speedier page loads.

Also new in Firefox 11 is add-on synchronization. For several versions now  Firefox Sync fully supported, and now your favorite browser extensions will automatically keep themselves lined up across all your installations.

Another key addition is support for Google’s SPDY protocol.
(The project was first announced way back in 2009 as a way to reduce page load times. It’s still not widely supported despite the promise of a 64% speed boost. A handful of Google’s web apps and services utilize SPDY when it’s available, including Gmail and Google-powered advertising.)

Also you can run your own Sync Server for different PC and Devices