I agree. Maybe they could differentiate the two versions with a badge or some adornment in the UI which appears grayed out in the “free” edition. I guess it’s the same as asking for donations but maybe not as blatant. Also not sure why they stopped selling merch. I would buy some right now.
To have a premium product, you need to have a non-premium product, and given that most users would use the non-premium product, firefox would quickly become associated with a browser that has the actually desirable features turned off...
Which would probably be even worse than their low market take up at the moment (and I am typing this on firefox).