This addon needs the companion app to work. There are false positives due to the heuristics used by the antivirus. This software is safe and Mozilla has the source code. A new version (1.3.0) will be listed soon to avoid the false positives.

https://www.virustotal.com/#/file/58ebe6f79158f892ca2963e57f8fa11ded73e69f2fbf587893b339cf288b97e0/detection