STR:
You might need to change 2 values in the about:config

1. devtools.application.enabled -> true

2. dom.ipc.processCount -> set to 1

3. Open https://serviceworke.rs/strategy-network-or-cache.html -> demo

4. Open the Application panel

5. Result: listWorker exception in the terminal log

console.error: "Error writing response to: listWorkers"
console.error: "Error while calling actor 'contentProcessTarget's method 'listWorkers'" "Component returned failure code: 0x80004005 (NS_ERROR_FAILURE) [nsIServiceWorkerManager.getRegistrationByPrincipal]"
console.error: "_getServiceWorkerRegistrationInfo@resource://devtools/server/actors/targets/worker.js:160:16\nform@resource://devtools/server/actors/targets/worker.js:48:33\nwrite@resource://devtools/shared/protocol/types.js:355:32\ntypes.addArrayType/write/<@resource://devtools/shared/protocol/types.js:220:33\nwrite@resource://devtools/shared/protocol/types.js:220:16\nwrite@resource://devtools/shared/protocol/types.js:379:22\nwrite@resource://devtools/shared/protocol/types.js:268:39\nwrite@resource://devtools/shared/protocol/Response.js:98:22\nwrite@resource://devtools/shared/protocol/Response.js:43:28\nsendReturn@resource://devtools/shared/protocol/Actor.js:164:38\npromise callback*generateRequestHandlers/</handler/<@resource://devtools/shared/protocol/Actor.js:186:14\n_queueResponse@resource://devtools/shared/protocol/Actor.js:107:22\nhandler@resource://devtools/shared/protocol/Actor.js:183:14\nonPacket@resource://devtools/server/main.js:1402:58\nreceiveMessage@resource://devtools/shared/transport/child-transport.js:66:16\nMessageListener.receiveMessage*_addListener@resource://devtools/shared/transport/child-transport.js:40:14\nready@resource://devtools/shared/transport/child-transport.js:57:10\n_onConnection@resource://devtools/server/main.js:963:15\nconnectToParent@resource://devtools/server/main.js:323:17\ninit@resource://devtools/server/startup/content-process.jsm:68:31\nonInit@resource://devtools/server/startup/content-process.js:25:5\nMessageListener.receiveMessage*@resource://devtools/server/startup/content-process.js:34:1\n"

:yulia: as you recently worked on this, would you mind giving us pointers on how to fix it? thanks! :)

I don't think I can help much here since the stuff I am doing is still a WIP, and it isn't related to workers but to processes. I think jdescottes might have more context.

My opinion is that this is the same as Bug 1564154, which is also the same as Bug 1447197.
Can we try to keep a single bug for this error?

I do agree it looks like the same bug, breaking different parts of the Application panel. Once Ola is back, we'll talk about merging the bugs.

Same as bug 1564154 - can't reproduce anymore.