Review Mozilla 1968048: Restore to only Normal Browsing Mode on cold startup

🔍 Bugzilla Audit

Bugzilla: https://bugzilla.mozilla.org/show_bug.cgi?id=1968048

Description

Return value of getModeFromIntentOrLastKnown was changed from settings().lastKnownMode to BrowsingMode.Normal. During the rebase I kept the change, but we should double check that is was the right call.

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information