What that entails:
"When performing a preliminary review, editors will review the source code for security issues and major policy violations, but will not install the add-on to test functionality in most cases. Preliminary review will be granted unless a security vulnerability or major policy violation is discovered."
Extensions marked 'experimental' are not fully reviewed. Which is why they probably left this plugin marked as 'experimental'.
You can't blame the users since they are installing from a Mozilla page and trusting the brand. I hope this triggers a review of those procedures at Mozilla, since I would consider sending back every site you visit a 'major policy violation'. Very scary.
Edit: they may also want to change the 'experimental' policy and set a time limit to how long an extension can remain experimental, and not list them in the default directory unless users (more advanced users) specifically seek out experimental extensions
I definitely agree with setting a time limit, if feasible.