It's important to note that the Developers Editions (and the Nightlys) will have a setting for disabling the requirement.
The assumption being that developers need to test as they develop. And are a more informed user.
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"There will also be special unbranded versions of Release and Beta that will have this setting, so that add-on developers can work on their add-ons without having to sign every build."
Developer edition is what used to be known as "Aurora", which is in between Beta and Nightly.