Mozilla had around $7-8 million in profit last I looked. Currently over $9 million. They could still afford them at $250k each. Such a project would've even been worth most or all of a year's profit. Fortunately, they're doing Quantum to improve things. :)
Revenue is the important number to look at - Wikipedia has it at $329.5M as of 2014. Profit is after salaries - when all the early Firefox people left, they were replaced by other programmers, who probably cost a bit less but not a whole lot. I think tsunamifury's estimate of $500K-1M minimum isn't out of line, but even then, a team of 20 people making $1M fully-loaded costs $20M, which isn't exorbitant. Mozilla's revenue was estimated at $57M in 2006.
