Extension.sys.mjs generates a random number at the startup of the first
extension, to have a shared secret (between parent and child processes)
serving as a key for a KeyedUUIDMapper in ExtensionDocumentId.sys.mjs.
This triggered a Talos regression because `crypto.getRandomValues()`
initializes NSS. This patch fixes the issue by replacing the call in
`Extension.sys.mjs` with a new alternative that is independent of NSS.
The `crypto.getRandomValues()` call in ExtensionDocumentId.sys.mjs also
switches to this new method, mainly for consistency (not to avoid NSS
initialization, because that already happens next in `gMapper.init()`).
Differential Revision: https://phabricator.services.mozilla.com/D309331
Rob Wu
31ca2d5f1d