Comment 3 for bug 443121

Thanks for the quick reply!

The amount of bookmarks indeed seems to be part of the problem, yet I also discovered something else.

First some information:
I have 78 bookmarks in total, in a hierarchy that is two subfolders deep. The actual json-bookmark file exported by Firefox is 33KB in size.
My Internet connection is not very fast (max. 15KB/s upload).
I waited 15 minutes to see whether the initial sync would eventually complete, but this was not the case and Firefox was still unusable after all the time.

So I deleted all bookmarks. With nothing to sync, the browser now was usable from the start.
Then I restored my bookmarks, by loading a backup file from within Firefox.
Interestingly, this time the browser remained usable, beam.smp and firefox did not consume 100% CPU, and the sync began, at a rate of about 1 bookmark per minute.
There were no errors and warnings in the error console, only regular messages about the ongoing transfer. It would probably have completed successfully.

But out of curiosity I did not wait that long. Instead I restarted Firefox, with the result that, once again, CPU load spiked and the restarted browser froze.

In short:
-Start Firefox+Bindwood with existing bookmarks --> freeze, high CPU load
-Start Firefox+Bindwood without bookmarks, restore them from file --> regular sync begins

I also tried to get debug information according to your instructions. But with the browser frozen I was unable to access the error console.