Works wonderfully on Firefox 91 (July 2021). Great extension.

All hail Mike Conley!

https://bugzilla.mozilla.org/show_bug.cgi?id=17754#c177

Thank you for a wonderful add-on.
I was troubled because tab submission could not be used with firefox 57.

Thanks for extension, it is so useful for me! And seems it works with Middle mouse click - opens new Firefox tab for submit. So please describe this in extension description