> I have no sense of what they stand for
There a nice Mozilla Manifesto explaining the Mozilla mission and their values [1].
Apparently, it's difficult to find a stable, independent, and effective revenue model for an open-source browser that is completely free as a product, should not contain shady ads or product promotions, does not sell user data, and always puts the user first.
This is especially difficult because there are other free browsers with a similar mission that don't need to incur the cost of developing their own web engine.