I made a quick test and I see that there is no direct relation between the number of tabs and the processes. It probably uses them as a pool of processes.
Yes, later I noticed that even with multiple pages open the number of active processes does not increase.
The main question would be what are so many processes for since killing 3 of them seems like Firefox is running smoothly anyway.
Won't they be useful for spying on the user's actions (sending information secretly)?
In this regard (I should open another thread), I think many of us trust sw which source code is also provided; but who assures us that the compiled and actually used version is the same as the source provided?