If Mozilla operates from revenue derived from selling www traffic to an advertising company running a "search engine", then it is 100% possible and realistic that Mozilla's browser could be optimised for advertising

Mozilla literally advocates for an "online advertising ecosystem"

At present Firefox is designed to send search traffic to Google by default

Mozilla can only see its continued existence through support from advertising. It does not just partner with advertising compaines, it actually acquired an adtech company

Google has a history of "shaking the cushions" by targeting their advertising customers and Chrome. It's reasonable to forsee that they could also target the agreement with Mozilla, i.e., Firefox

https://www.inc.com/minda-zetlin/google-found-a-sneaky-way-t...

https://nypost.com/2023/11/29/business/google-ad-chief-jerry...

Maybe Mozilla breaks its partnership with Google, who knows. But based on a long history of Mozilla advocacy for online ads and working with online advertising companies, it seems 100% committed to online advertising as a "business model" regardless of whether it partners with Google or another "search engine"