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This PR fixes Companion in Firefox 85 (and 86 Nightly) and closes #955
Underlying issue
Based on my debugging session with Firefox Nightly stopped leaking unique extension ID via Origin header. Probably to reduce the surface for fingerprinting, which is pretty funny considering that around v72 Chromium moved... in the opposite direction: Chromium was sending anonymous
Origin: null
and now v86 sends extension ID instead 🤷♂️Overall, the behavior of
Origin
HTTP header in XHRs coming from within browser extension is not reliable: vendors change this behavior back and forth, often contradicting each other.Fix
Refactored the way we detect requests coming from the Companion extension to be independent of the brittle Origin HTTP header – instead, we now inspect requests via lower level WebExtension API and updated + added new tests for both Firefox in Chromium variants.