#6267 Fix Firefox content script sandbox bug

[martgil]

This PR attempts to fix the Mozilla Firefox content script sandbox bug where Permission denied to access property "autoAllocateChunkSize" error occurs.

close #6267

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Tests (delete all except exactly one):

• Does not need tests (refactor only, docs or internal changes)

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To be filled by reviewers

I have reviewed that this PR... (tick whichever items you personally focused on during this review):

• addresses the issue it closes (if any)
• code is readable and understandable
• is accompanied with tests, or tests are not needed
• is free of vulnerabilities
• is documented clearly and usefully, or doesn't need documentation

[martgil]

Converting to draft as I have shared the built Firefox browser extension directly from this PR to the user to test it out first.