I don't want to offend the extension creators, I want to option to uninstall an official extension and put my own or a community one but IMO there are reasons to trust Mozilla then a stranger or a community. There were cases where popular extensions were bought and updated with malicious code, because of that I make sure I open bank or paypal website in a private window with extensions blocked but will a regular user know to do this ?

One could always stick to open-source extensions... if Google didn't make developer mode such a painful experience.

I don't think it is about who you trust but who can resource the amount of work required to keep it going? There are thousands of browser extensions, including all of their updates etc.