Firefox is close to crashing and burning, but it'll take long enough that there is hope Servo or Ladybird will be more viable replacements by then. (even though ladybird leadership aren't exactly trustworthy, it's still an open project with good tech).
Also, if you ask me, "Firefox spends X million dollars" isn't necessarily a fair measure of how much it costs to maintain a secure browser, we know that Mozilla is managed inefficiently and an alternative might not be so impossibly costly.