Firefox was mostly funded by Alphabet/Google to avoid antitrust lawsuits/promote their search engine, one of the best scenarios for the "big corpo" is a product (firefox) that doesn't have many users and cater to the most anti-corpo users (users that wouldn't like to use "big corpo" products anyway). At this point mozilla is just a bussiness expense for the big corpo, the cost of doing bussiness.
"Big corpo" can argue, "look we are even funding the competence", the competence need to be small but relevant enough, so while you are thinking that you are fighting the "big corpo" the reality is that you are just helping to keep firefox relevant enough that the "big corpo" can't be sued.