I guess I'm wondering primarily what "democratically controlled" even means. Like everyone votes on every decision? Or we elect people to make decisions? Or we vote on "big decisions"? (Who defines "big"?
Most companies are democratic. In the sense that the shareholders appoint the decision makers. Shareholders -> Board -> management.
Your point about "worker owned" simply means the workers own the shares, and hence "democratic" would seem to be redundant. Unless you are suggesting that the democratic function is exercised in another way?
Now clearly Mozilla is a mix of non profit and for profit. A non profit doesn't really have shares (there's usually some other approach to appointing decision makers.)
So, I think you are suggesting that the voting rights move from "shareholders" to employees.
Naturally this opens the door to 51% attacks, or more specifically incentivises workers to coalesce into groups with mutual-support voting.
Given a reasonably high turnover in workers, we should therefore expect decision making to be mostly short-term not long term? (Simplistically, most people will vote to further their short term returns, ignoring long term goals because in the long run they're not here.)
In other words the company starts to behave a lot like a govt does. Regular elections promote short-term goals and results (don't start a project that will complete after you've left) at the expense of things like maintainence etc.
It also values political skills over say engineering skills. Being a good speaker counts for more than being competent.
Do you believe this structure will make a better browser? When funding runs low, will they make better decisions on which staff to cut?