This add-on is good for TRANSFERRING bookmarks from on browser to another, once only, as long as you have substantially fewer than 15000 bookmarks total. (Which for anyone who's been on the Internet for more than a few months, is a pathetically small number.)

However, it sux at SYNCHRONIZING bookmarks, because of two huge problems:

Firstly, even if you only have about 7000 bookmarks, you'll run into "quota limits" causing an incomplete upload of bookmarks, because the "quota" adds all existing bookmarks on the server, all "backed-up" bookmarks on the server, all bookmarks on machine-to-be-synced-#1, and all bookmarks on machine-to-be-synced-#2, and insists that THAT TOTAL must be < 15000, which of course it won't be: it'll be 20000 or 30000. So, you get incomplete (50%? 25%? 10%?) synchronization.

Secondly, this add-on has the infuriating habit of duplicating all of your directory structures (but none of the actual bookmarks) in your main computer's "Bookmarks" menu, creating an ungodly mess requiring hours to carefully find and erase all of the hundreds or thousands of bogus empty folders. And then it'll do it again the next time you try to merge. And again. And again.

In short, nice bookmark FORWARDER, but NOT a viable bookmark MERGER. I'll be nice and give it 2 stars out of 5 (though, arguments could be made for giving it 1 or 0 stars).