Thanks for making the switch. Duplicate detection is a planned feature, and I'll definitely work on adding it to the next iteration of Freezetab.

Cloud syncing is certainly on my radar, but slightly more difficult. If Freezetab synced the saved links with Google Bookmarks it would lose all the metadata associated with each link. Freezetab assigns each saved link a unique ID for example — bookmarks don't allot any extra storage for this sort of custom metadata. I do plan on building a server side implementation of Freezetab to handle syncing if the extension gains enough traction.