Is it "sabotage" when you don't intentionally devote resources to making some random third party's browser work? What obligation do they have?
Mozilla has cachet with nerds like us because of its history. Not because it's particularly better than alternatives or because it has enough of a user base to throw its weight around.
In contrast, they do test on Safari. They'd lose double-digit percentages of users if they didn't.
The ecosystem, unfortunately, generally has room for three top browsers. I'm not even sure Firefox is number four these days.
