You can be both things. Generally it's nice to be paid for your work.
"The restrictions (based on security reasons) to install an extension from a site different than mozilla addons"
If someone convinces you to install a malicious browser extension (easily done in a world where people will click OK on basically anything) they can spy on and control everything you do online.
Do you think then that for example desktop software must be installed from a central company like Microsoft because someone can convince you to install it from every website?
And also: do you think that Mozilla was really doing security inspections in the early days? No, it wasn't, the extensions had all kind of security bugs. I think it was more about control.
You can think it was about control, but this could not be farther from truth.
<disclaimer>I work for mozilla</disclaimer>
There are alternative methods that Mozilla could do, like bringing a Mozilla certificate to host the extension in your own site without an extra prompt.
You are talking around the larger problem, which is a huge one for many extension and app ecosystems (e.g. Google Play, where weak-AI scanners fail to stop malware and spamware).
Mozilla uses community review, which works much better but is of course imperfect, a human thing.
No one that I know of has solved this larger problem. I would be interested in research pointers and tips (not complaints).
/be