And it's their browser, which they have an interest in. If an extension goes rogue and gets in the news, that would be bad for a variety of reasons.
You're right that it's your computer, and you're free to change and recompile Firefox to do whatever you want, so I don't see what the issue is. The polices are for what extensions they allow on their store not what you can install on your computer. Last I knew, you could make your own extension and load it yourself with the store being involved at all. Go nuts.
That attitude is exactly the problem. There is zero reason for anyone to use Firefox if its just another company's property and not a free and open piece of software.
You're right that it's your computer, and you're free to change and recompile Firefox to do whatever you want, so I don't see what the issue is. The polices are for what extensions they allow on their store not what you can install on your computer. Last I knew, you could make your own extension and load it yourself with the store being involved at all. Go nuts.