Rated 5 out of 5 stars

If you have problems after the update:

1. In case your Firefox is blocked by an Xmarks pop-up: Restart Firefox and quickly go to your add-on list. Then disable add-on Xmarks and restart.

2. If you use NoScript, go to 'Options' > 'Whitelist' and allow xmarks.com and add googleapis.com to the list

3. If you use RequestPolicy, go to Preferences > Whitelist and add xmarks.com in 'Origins', and add googleapis.com in Destinations

4. In NoScript, choose 'Allow Scripts Globally'

5. Re-enable Xmarks and restart Firefox.

6. Now sync your bookmarks with Xmarks. If Xmarks asks to login, enter your login data for your Xmarks account.

7. In NoScript, switch back to 'Forbid Scripts Globally'.

Everything should work again.

This review is for a previous version of the add-on (3.7.8).  This user has other reviews of this add-on.