Our first-party isolation patch incorrectly rejects blobs retrieved in workers
When isolation is enabled, blobs retrieved by an XHR inside a worker are rejected even when the blob's first party matches the worker's first party. I found that the regression was caused by this Mozilla patch: https://hg.mozilla.org/mozilla-central/diff/12a852867c16/dom/base/nsXMLHttpRequest.cpp#l1694
Because of the Mozilla patch, when we are in a worker, NS_NewChannel is no longer passed a document, so our patch code in nsHostObjectProtocolHandler::NewChannel2 is not able to obtain the correct first party. Therefore the blob URI is rejected even if the first party of the worker matches. I haven't yet figured out how to fix this problem.
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