You seem to be unaware that intelligence services have been hoovering up internet traffic wholesale for decades, and that telcos do it internally as well. Verizon's "supercookie" is a great example.
On the other hand, if intelligence agencies are personally targeting you it's already over. This might help them, but even they can probably get everything they need on you with way less effort.
But Mozilla is not a government agency or a telco.
Are government agencies somehow restricted to compromise telcos but not any other organization?