I think you are comparing Apples with Oranges. Linux organizations are mostly done by volunteers and most of the infrastructure used is either donated or allocated in organizations which support their development. So any costs they have is for maintaining anything they really have to pay such as: legal, taxes etc...

On the other hand Mozilla has to pay for infrastructure (and here they have to support multiplatforms and multi OS developments), development, legal, taxes, marketing etc... etc.. It's not even comparable in any order of magnitude the costs involved.

If Mozilla would be to survive with volunteers would be even more miles ahead of other browsers. You can see Thunderbird as an example that Mozilla stopped maintaining since years the development pace slowed considerably.

On a side note: I really wish for the sake of the internet that Mozilla gets their s* together and start to improve their products to be really competitors to Chrome and Safari.