EDITED: All my tabs are still there, the addon is perfectly working for me. But it seems it's not the case for most of the users here. I don't know why it's working for me, and not for other users. I suggest you to use another addon, that seems better now: better-onetab instead. Because Onetabe hasn't been updated since 2017, it really seems it's not maintained anymore!
My previous review: It doesn't lose your tab, and if you want to be sure it'll never lose any tabs, the extension lets you save them to the disk in a html format, very handy.
This is the extension I use to keep my sessions, close in one click the tabs when I have many many, and save them. One of the best memory saver.