Google Browser Sync for Firefox is an extension that continuously synchronizes your browser settings – including bookmarks, history, persistent cookies, and saved passwords – across your computers. It also allows you to restore open tabs and windows across different machines and browser sessions. The project is no more maintained, and will not see in Firefox 3. Thus it’ll only be available until the end of 2008.

Here's the message received from Google by an inquisitive user:

It was a tough call, but we decided to phase out support for Browser Sync. Since the team has moved on to other projects that are keeping them busy, we don't have time to update the extension to work with Firefox 3 or to continue to maintain it.

For those of you who want to continue to use Firefox 2, we'll maintain support for old versions of Google Browser Sync through 2008. After that, we can recommend a few other products that scratch a similar itch. We hope that one of them works for you:

• Mozilla Weave from Mozilla Labs - Offers bookmark and history synchronization across computers.
• Google Toolbar for Firefox - Store your bookmarks online and access them from any computer online. [although, this is not 3.0 compatible as of writing]
• Foxmarks Bookmark Synchronizer - Synchronizes your bookmarks across all computers where it is installed.

Source:→ Google System