Looks like this was an issue with my Browser Toolbox profile. I accidentally turned off
devtools.chrome.enabled, maybe via the DevTools settings?
And recently the debugger started checking the devtools.chrome.enabled pref in order to hide/show webextension sources in the debugger (release 121, PR https://github.com/devtools-html/debugger.html/pull/7705).
- it would be nice if the empty state for the sources pane was not a blank panel
- we should make sure that toolboxes that want to debug addons have this pref turned on. It is a bit weird, because it is a profile setting. And maybe you don't want to see webextensions when debugging regular pages, but you still want to debug extensions from about debugging.
Maybe we need a shared helper to know if webextension sources should be visible, and it could compute that based on a combination of this preference and "is the current target a webextension".
Overall the responsibility of devtools.chrome.enabled is a bit weird. It's mostly a client side preference (only used in the storage actor on the server).