[fullstory] can't access dead object TypeError

We are observing through Sentry that the FullStory integration has started to throw a TypeError: can't access dead object error for some users.

The error is happening on Firefox Version: 89.0, Windows Version: 10

This is the breadcrumb:

TypeError: can't access dead object
  at contentWindowDesc.get(blob:https://[REDACTED])
  at 727/mo</e.prototype.tellAllFramesTo(/s/fs.js:3:154263)
  at 727/mo</e.prototype.shutdown(/s/fs.js:3:154141)
  at 727/hs</e.prototype.shutdown(/s/fs.js:3:196647)
  at 727/hs</e.prototype.splitPage/</<(/s/fs.js:3:197338)
  at a/</<(/s/fs.js:3:3614)
  at a/<(/s/fs.js:3:3719)
  at h/<(/s/fs.js:3:2643)
  at h(/s/fs.js:3:2388)
  at 727/hs</e.prototype.splitPage(/s/fs.js:3:197117)
  at splitPage(/s/fs.js:3:202919)
  at 727/Co</e.prototype.enqueueEvents(/s/fs.js:3:165233)
  at 727/Ni</e.prototype.processEvents(/s/fs.js:3:134713)
  at 727/Ni</e.prototype.startPipeline/</</<(/s/fs.js:3:131715)
  at 727/yn</t.prototype.start/<(/s/fs.js:3:42885)
  at e/this._wrappedTick<(/s/fs.js:3:41483)
  at ce/<(/s/fs.js:3:19725)

The report points to the FullStory integration's bundled /s/fs.js, where contentWindowDesc.get is reached during tellAllFramesTo, shutdown, and splitPage. Start by tracing this Firefox 89 failure in the integration source and determine the expected handling of dead objects. Done means the error no longer occurs for the reported Firefox and Windows case, with verification covering the affected flow.