Source: http://lifehacker.com/5512326/xmarks-for-firefox-syncs-open-tabs-between-browsers
Firefox: Fans of the Xmarks bookmark and password syncing service, rejoice. You can now close down any Firefox browser connected to Xmarks and open whatever tabs you left standing on another browser. It's a nice little bit of worry reduction.
Mozilla's own Weave tool added tab syncing in its 1.0 release, so its nice to see Xmarks catch up to the competition. But given that Xmarks works, in one form or another, across Safari and Internet Explorer as well, a future update could make tab syncing much more convenient for the home/office divide.
To get the tab syncing, you'll have to download the preview version of Xmarks' add-on from the blog link below (or grab it here, directly), or wait about a week for the update to show up in Mozilla's add-on repository. Head to your Xmarks settings in the Tools menu, enable tab syncing, and give the Firefox setup and computer you're currently using a name. Do likewise on other computers you've installed Xmarks on. To retrieve single tabs or whole sets from other browsers, head to the Tools menu, open the Xmarks sub-menu, and choose "Open Remote Tabs."
Xmarks states that it uploads your window and tab status in the background, when your browser has a "quiet moment," so it might not always pick up every last tab, especially before a crash. It is, however, a nice piece of mind that costs you nothing. Xmarks is a free download, works wherever Firefox does.