Same problem with Firefox 78.7.1, starting without any caches, (https://share.firefox.dev/3bAiAJO) where releasing cache write output stream is locked multiple times and takes too much time.
Bug 1693810 Comment 2 Edit History
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Same problem with Firefox 78.7.1, starting without any caches, (https://share.firefox.dev/3bAiAJO) where releasing cache write output stream is locked multiple times and takes too much time. If caches are already there, everything is OK : https://share.firefox.dev/3dDA5eR