I can reproduce this fairly reliably (> ~50% of the time) in debug builds on Nightly. It seems more rare in opt builds (but I haven't done as much testing there). Sometimes I get an error in the Browser Console when closing it, after which it will not re-open (no error shown when attempting to re-open, though).

The error is not always the same, here are the ones that I've captured:

JavaScript error: resource://devtools/client/webconsole/webconsole-ui.js, line 390: TypeError: can't access property "resourceCommand", this.hud is null

JavaScript error: resource://devtools/client/webconsole/webconsole-ui.js, line 145: TypeError: can't access property "dispatch", this.wrapper.getStore() is null
JavaScript error: , line 0: NotFoundError: No such JSWindowActor 'DevToolsFrame'
JavaScript error: , line 0: NotFoundError: No such JSWindowActor 'DevToolsFrame'
JavaScript error: , line 0: NotFoundError: No such JSWindowActor 'DevToolsFrame'
JavaScript error: , line 0: NotFoundError: No such JSWindowActor 'DevToolsFrame'
JavaScript error: , line 0: NotFoundError: No such JSWindowActor 'DevToolsFrame'
JavaScript error: , line 0: NotFoundError: No such JSWindowActor 'DevToolsFrame'
JavaScript error: , line 0: NotFoundError: No such JSWindowActor 'DevToolsFrame'
console.error: (new TypeError("can't access property \"top\", props.toolboxDoc.defaultView is null", "resource://devtools/client/shared/components/menu/MenuButton.js", 111))
console.error: ({})

(The JSWindowActor thing appears to be unrelated, or at least not directly at fault - I sometimes get it without the Browser Console breaking.)

https://hg.mozilla.org/mozilla-central/rev/7ecc8473d530

Should we request for an uplift since 104 (and 103) are likely to be affected?

Set release status flags based on info from the regressing bug 1764348

Comment on attachment 9289392 [details]
Bug 1781269 - [devtools] Don't try to unwatch resource in stopWatchingNetworkResources when Console is closing. r=jdescottes.

Beta/Release Uplift Approval Request

• User impact if declined: The user may not be able to use the Browser Console
• Is this code covered by automated tests?: No
• Has the fix been verified in Nightly?: No
• Needs manual test from QE?: No
• If yes, steps to reproduce:
• List of other uplifts needed: None
• Risk to taking this patch: Low
• Why is the change risky/not risky? (and alternatives if risky): Small, DevTools change only, adding a simple guard inside the function that was causing the issue.
• String changes made/needed:
• Is Android affected?: No

Comment on attachment 9289392 [details]
Bug 1781269 - [devtools] Don't try to unwatch resource in stopWatchingNetworkResources when Console is closing. r=jdescottes.

Approved for 104.0b9

https://hg.mozilla.org/releases/mozilla-beta/rev/573ec4e35374