Earlier quoted context omitted.
Just never allow such a transfer force a new user to create a new name. Ensure this is part of the terms of service. Prosecute violators that is to say buyer and dev under cfaa and ensure a hefty fine is levied with prison time. Nefarious parties will find few sellers thereafter.
As long as an extension can be owned by a company, you can bypass restrictions on transferring the extension by transferring ownership of the company. Unless you think plugins for HTTPS Everywhere, Google Translate, and LastPass should be signed by an individual developer - in which case you'll have to solve the problem of what to do when that developer moves between jobs :)
A buyer company or individual ought to have to create a different name and convince users to install/trust their extension if ownership is transferred instead of merely taking control of the existing name and having the next automatic update install malware.
Extension systems and language specific package managers on the overall have garbage security and are going to be a way bigger problem in the future. They are low hanging fruit.