Firefox's Extensions ("add-ons") debugger changed a few releases ago, and it's not working for me at all; it's not finding my extension's sources.
Following the instructions at https://extensionworkshop.com/documentation/develop/debugging, I went to the about:debugging page, loaded a "Temporary add-on", and pressed the "Inspect" button. Once there, I saw a whole lot of nothing, plus the helpful message that "This page has no sources".
The extension itself (it's the super-simple example provided by Mozilla that just puts a colored border around any page) works fine.
So why doesn't the debugger see it?
I do see other questions at stackoverflow about "no sources" but they were posted before Firefox version 69 (which is when the new debugging interface appeared), and they aren't really shedding any light this problem.
I'm running Firefox 70.0.0.1 on Linux, FWIW.