There are only a few options here.
You can file the ticket claiming that the shiny new promoted thing is actually an antifeature and that you hate the popup. You can then hope that the PM or exec who is currently receiving adulations or making speeches in the hope of a bonus or promotion after the rollout gets assigned the ticket, rather than some lowly volunteer. Then, the next time they get asked to make something, they'll think "wait, maybe I shouldn't advertise this new thing by forcing a popup on every Firefox user?" If that happens often enough to become part of the shared zeitgeist at the organization, they may be able to enact a Mozilla-wide policy against such popups and stop building antifeatures. Good luck, I hope it works for you.
Or you can throw sand in the works. When the accessibility department complains that people keep filing tickets and wasting their time whenever a new feature includes a popup, that component of the organization can push back
Every time I inadvertently find myself at a gas station with those horrific advertisement kiosks installed at the pumps, I either look around for a nearby station that doesn't have ads playing, or I stab the "Help" button to page the cashier. I am well aware that the minimum wage employee stocking the shelves and helping people prepay does not have the phone number of the GSTV producers or the executive decision makers at ExxonMobil or whoever, and I have no animus against that person - I'm infallibly polite with the individual. But I ask them to keep the line open to mute the ads, and they usually do. My only hope for eliminating those ads is either shopping at different gas stations - but how are they ever going to distinguish that microscopic boycott from the noise - or hoping that this communication filters up through the organization.