Hi, there are two known issues in Tab Stash which can cause high CPU usage (see my replies to the other reviews below). However, resetting Firefox should address both issues. So, since you have reset Firefox, I would hope and expect you won't see high CPU from Tab Stash again.

However, if you do notice high CPU usage even after resetting Firefox, please feel free to open an issue on GitHub and I'd be happy to troubleshoot with you further.