It does create a conflict of interest, and a significant risk that at some point greed will win - compare e.g. AdBlock Plus that started with the "acceptable ads" program and then allowed the worst of clickbait (Taboola & Co.) despite heavy user complaints.
On the other hand, it also provides an opportunity to have a trusted addon ecosystem. If the price is reasonable, popular free addons can collect it through donations, and in exchange, users can be sure that the addons were actually reviewed (hopefully thoroughly and by humans, i.e. with a much lower "oops bad thing slipped through" rate than addon stores that rely mostly on automation).
Could even be a great way to generate revenue. Have two versions of the addon. One is free. One costs $1/year but is reviewed. Same addon. I know which one I'd pick (for myself and all relatives). Mozilla and the addon dev can split the revenue 50:50.
On the other hand, it also provides an opportunity to have a trusted addon ecosystem. If the price is reasonable, popular free addons can collect it through donations, and in exchange, users can be sure that the addons were actually reviewed (hopefully thoroughly and by humans, i.e. with a much lower "oops bad thing slipped through" rate than addon stores that rely mostly on automation).
Could even be a great way to generate revenue. Have two versions of the addon. One is free. One costs $1/year but is reviewed. Same addon. I know which one I'd pick (for myself and all relatives). Mozilla and the addon dev can split the revenue 50:50.