This addon does not even do what it advertises. It works OK as a bookmark manager within multiple instances of Firefox or Chrome, but this is completely unnecessary and redundant as FF and Chrome both have bookmark syncing (and so much more) built in when you log into a Mozilla/Google account. Backup and restore is neat, but again, this is also redundant as these feature already exist in the browser. If you are reading this and are considering EverSync as a way to sync between Chrome and FF, this is not the tool for you. I attempted to do this multiple times over a 6 month period, trying different methods, and it all it would do was lock up FF/Chrome on me. Also, be aware that you need to purchase a premium account ($44) to have it do over 1,000 bookmarks. Also be aware that when you purchase this with PayPal, it is an annual subscription that will automatically renew each year until you cancel the subscription with Nimbus and/or remove the per-approved payment from PayPal.
EDIT: Nimbus was nice enough to give me a partial refund of $40 when the subscription renewed this year. I had forgotten all about it. I am very grateful for that. Thank you Nimbus.
EDIT: Some of the issues with the bookmarks may be partly to blame on the browsers themselves. I have experienced some lockup issues in FF and Vivaldi (a Chrome fork that is very buggy, I have since uninstalled it) when exporting/importing my bookmarks. I have thousand, possibly tens of thousands of them, most work related. I am going to look for alternative solutions to this, like maybe some sort of cloud based "bookmark" option.