Hello,

The issues with double-tabs being opened seems more like a Firefox issue, so far nobody reported such issue (and I get a lot of e-mails :)).
You may want to use Firefox Reset feature to fix such issues:
https://support.mozilla.org/en-US/kb/refresh-firefox-reset-add-ons-and-settings

Regarding reloading thumbnails - this is a tricky thing to do now since creating thumbnails in background is no longer possible in new Web-extension API. So reloading thumbnails gets interrupted if you close or switch tab. Auto-reload with "almost background reload" is coming in upcoming weeks.

If you experience more issues, please report them to my support e-mail. I'm fixing bugs sometimes within 24 hours.

I'm sorry for the inconveniences.

Have a nice day :)

Best regards,
Juraj Mäsiar