Browsers shouldn't require accounts, and thankfully Firefox doesn't. But having a way to synchronize my passwords across all my devices is pretty important.
They had an implementation that did not require any accounts. They deemed that it's too confusing for users* to scan some QR codes (or type a bunch of characters), so they went with an account-based system.
*) Or whatever the real reason was. It was about time Mozilla started to have management issues so I absolutely won't be surprised if the goal was to "become an ecosystem" or "gather a userbase" (or whatever is management speak for forcing people to sign up).
> scan some QR codes
How is that not still an account? What definition of account are we working with here?
Maybe it was using technology similar to magic wormhole.