Thanks for responding, and all the work you do!
I eventually just switched to using another browser, since I did not want to delete all of my other browser data. I also had been doing all of my plugin development using developer mode already, loading in the addon files from the localhost folder on my machine.
What roughly happened was I started developing with my addon.json id value set to something like "AbC" and then because of some issues switched it to "abc", which triggered this error. Changing it back to "AbC", and reloading afterwards, did not result in this error going away, which just resulted in a dead end.