Hello,
It depends on the point of view :), I can see the source code just fine.
Seriously now, I've spend countless hours implementing this addon (and many other addons) and it's completely free.
Is that not enough?
Imagine if you did something free for others and people would still complain. It's discouraging.
Note that Mozilla reviewers can also see the original source code (for all of my addons) so they are safe to use.
Best Regards,
Juraj Mäsiar