Current 2.0.0 version is very buggy and not usable:
- It has problems with local Firefox urls like about:preferences. If you have left open those urls it will brake all of it.
- It loads some tabs randomly as a junk urls.
- It reloads ALL tabs when switching and not only the active tab in that group

Better use some other addon until waiting for Tab Groups Reloaded or similar version to be ported for Firefox Quantum.