Hello Yofi. A few did report a similar behavior on specific environments. To help me debug it: Is your firefox sync on? - Its able to sync your bookmarks etc..?

I may have found the issue. Its a limitation with the storage amount firefox sync provides. Implemented a compression/decompression and chunking fix for it. Should be out with 1.5.0 version. I would be glad if you can update/install it, try it once and drop me a note.

1.5.0 is submitted. Should be available in an hour or two.