Fix Firefox, add build bits, etc

[half-duplex]

• Add Makefile to easily produce Chrome and FF packages
• Fix styling on Firefox
• Fix settings storage on Firefox
• Rearranges settings for clarity
• Fixes http and broken links
• Refactors "Vol" variables for consistency (doesn't change storage name)
• Uses Fixes issue #14 with last set volume not getting saved #19 (merge that first)
• Mention custom domain limitation (possible future enhancement: optional all_sites?)
• Etc

Smoke tested in FF and Chrome. It looks like the existing AMO package is a somewhat diverged fork last updated 3 years ago that doesn't match any styling. If they aren't around to update it, could one of us repost it?

[helloitszak]

It's funny I was just talking with some friends the other day about wanting to try and fix this up. Maybe I have a breach somewhere 😉

I'll try and get this merged this week and fix #29 in the process.

I don't know who maintains the current FF package, I believe it was forked off of this awhile back and maintained completely separately. From some googling I think it's @DanielKamkha who maintains it? I don't use Firefox as my daily driver, but I'm not opposed to putting this up on AMO. With Safari and Edge using the same format too, I might try to release a build for those as well.

Thanks for the contribution, this was just the extra kick in the pants I needed to fix the other stuff.

[half-duplex]

👍
See how that looks inheriting the text color as a <span> - tests: light dark black

Also, I set the addon ID to bandcamp-volume@itszakko so sync storage would work, idk if that should be something else. (If DK publishes these, it should probably that ID?)