1. History of installing and running arbitrary code on clients in the name of "Experiments" without user permission.
2. Full telemetry on by default.
3. Shoving their products like Pocket (added to the address bar by default, shows up as an advertisement on the page that opens after Firefox updates itself), Mozilla VPN (non-removable advertisement on every Private Window you open) in the name of revenue, while their clueless leadership enjoys fat paychecks for whatever value they bring to the organization.
4. Forcing undesirable changes down people's throat (removed the "Compact" density address bar after a redesign, hiding it under about:config).
Feel free to pile on.