Inspect is flaky in Firefox

[tomByrer]

Description Sometimes Inspect won't work in Firefox, & gives an intization error:

TypeError
can't access property "postMessage", targetWindow is null
send@https://o4dps.csb.app/node_modules/
xstate/inspect/es/index.js:152:13
evaluate/inspectMachine<.on["xstate.inspecting"].actions</<@https://o4dps.csb.app/node_modules/
xstate/inspect/es/index.js:111:22
evaluate/inspectMachine<.on["xstate.inspecting"].actions<@https://o4dps.csb.app/node_modules/
xstate/inspect/es/index.js:110:40
evaluate/Interpreter.prototype.exec
https://o4dps.csb.app/node_modules/xstate/es/interpreter.js:547:16
evaluate/Interpreter.prototype.execute
https://o4dps.csb.app/node_modules/xstate/es/interpreter.js:159:14
evaluate/Interpreter.prototype.update
https://o4dps.csb.app/node_modules/xstate/es/interpreter.js:179:12
Interpreter/this.send/<
https://o4dps.csb.app/node_modules/xstate/es/interpreter.js:92:15
evaluate/Scheduler.prototype.process
https://o4dps.csb.app/node_modules/xstate/es/scheduler.js:59:7
evaluate/Scheduler.prototype.schedule
https://o4dps.csb.app/node_modules/xstate/es/scheduler.js:43:10
Interpreter/this.send
https://o4dps.csb.app/node_modules/xstate/es/interpreter.js:89:23
messageHandler@https://o4dps.csb.app/node_modules/
xstate/inspect/es/index.js:156:22
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Expected Result Work as well as it does in Chrome. If I close the error window, then resize the browser, then that forces a refresh & the Inspector does work.

Actual Result

Reproduction https://codesandbox.io/s/xstate-inspect-no-child-o4dps

Additional context Firefox v82.0b1 I'll update later ;)

IMHO this is low-priority; even though I use Firefox for webdev, <10% of devs do, so I'm in the minority.