This reverts commit 350b256722.
Reason: buildbots were failing to compile new FF because their
cbindgen was outdated. This is now fixed on both Mac & Win.
Review URL: c3a577c46d
With this roll, Firefox has DocumentChannel enabled by default in Desktop Firefox:
- https://phabricator.services.mozilla.com/D57898
DocumentChannel, unlike nsIHttpChannel, doesn't have a `channelId` that we
can use to attribute navigation requests (see
https://github.com/microsoft/playwright/pull/249).
The feature has to be disabled for now in PlayWright with the
`browser.tabs.documentchannel` pref until we figure how to support it.
