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

Doesn't seem to work (68.0.1)

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

There's a website I use where I frequently middle click the submit button to submit forms to new tabs, so this add-on is essential for that.

The main issue I encountered is that this was triggering the popup blocker in Firefox 57. I had to add the particular website to my popup whitelist to get middle clicking buttons working as desired.

+ opens forms in foreground tabs
+ e10s compatible

- I can't get it to open forms in background tabs (that's my usual usecase - click multiple formsubmit buttons on the same page, rapidly)

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