It shows a clear case of mission statement in conflict with business model and shakes my confidence of Mozilla as the champions of privacy and freedom they paint themselves as.
Keep in mind that they don't even need to make it built in, they could instead bundle ublock origin as a preinstalled add-on and provide a little bit of money to the developer. It would simultaneously improve the security and browsing experience of many of its users while attracting many new ones and funding the fight against invasive online advertising.
But big daddy Google would get so cross then and Mozilla would be forced to adopt an actually privacy respecting alternative like duckduckgo and lose a lot of their funding.
I don't want to main Brave as I currently do, both because of its use of chromium and my ill feelings of the CEO's donations to political movements against the LGBT community but Mozilla management have lost my confidence over the years despite the actual deveopers remaining world class.