This is mostly in regards to eg.: Bypass Paywall extension, but it could very well be applied to any others in the future (and has in the past). Certainly could apply to eg.: uBlock Origin in the future.
We know big corporations will use the DMCA to try and take down anything that even remotely threatens their interests. We saw the examples of youtube-dl, for one.
We also know, from a few of the latest cases of DMCA request, that the requests are not made by actual humans but rather by AIs which provide a lot of false or misleading information, or can just be fired en masse against random internet targets, and there is a lot of chance these takedown requests are actually illegal (and the DMCA does allow for an illegal takedown to be challenged) since, by definition, an AI can not legally represent the interests of a copyright owner (and the takedown requests are not being used for that, anyway).
While normal users are in no condition to challenge those requests, Mozilla is, and as an organization that says to fight for a better web as well as the concerns of its users for safety and privacy, it should take a more participative stance in fighting the application of oppressive law. See for example the work of the OTW (Organization for Transformative Works) in this regard.
Ultimately this also affects the final users, as once an extension is removed from AMO by a corporate party strongarming Mozilla, those extensions are not normally installable by users, requiring them to go through a number of hoops, switching from stable channel to dev channel, etc.
