I never had any problems when developing locally (used jpm run and was even able to drop the .xpi file on the add-ons page and run it from there), and the extension went through review and seemed to have worked there as well.
I’m not sure what the problem is. The question is very broad. As a dev you’ll have to do the regular dev stuff. Try installing it and watching the messags in browser console. Add extra console.log’s and watch it. etc till you pin point it.
I did try installing your addon and it worked for me. But this is the case with many hard to find bugs. It happens on only certain configurations/computers. No choice other then to reproduce it first, either with new profile and trying to match conditions, or VMs, or other computers.
Aside from installing, I did have an issue opening your prefs page: