I just tried. It doesn’t work. As @jamesw@beehaw.org pointed out, it needs to be a FQDN.

It worked, although it’s not really how I thought it was going to work. Using browser.fixup.domainwhitelist.*.mysuffix doesn’t work.

I hope they add this feature into Firefox, although I don’t think that’s going to be the case, given that the issues you cited are 3 years old at the time of writing this.

Well, I guess it is what it is. Thank you!