Web extensions are pretty much limited for now, probably there will be some way to sync with other devices, or bookmarking options, in the future, but for sure it won't be soon. openerId is in the works by Firefox folks, it will start working as soon as it's implemented in Firefox, so be patient it will be there.
I will hide tab bar as soon as it will be available, there is an experimental API in the works as well. I have an update in the works to sync tabs on top, so ctrl+tab will work as it should.

I do my best to get all the kinks out.