Why Firefox starts and runs continuously multiple .exe processes consuming innecesary resources?

[robertotait]

From many years ago, my browser client Firefox continuously does the same: I use few tabs, usually with low operation in addition, but it ever opens a multiplicity of process with exaggerated and inexplicable resources consumption, tending to occupy all existing capacity.
It would be interesting, at least, to know the reasons.
(It runs nowadays over Windows 10 with an Eset Smart Security Premium payed license).

[StevieB]

I, too, am curious as to why I sometimes have either eight (8) or even ten (10) running when I have just one FF web page open.