This argument seems bizarre to me considering the volumes of money banks work with and the lack of programmers who only use banks that take Firefox. I'm not sure what you're expecting, that banks are just doing it to spite Mozilla?

I really don't believe the return-on-investment for a major bank to support Firefox is negative. Quick Google napkin math says a customer is worth $500/year, and a decent programmer is easily available for $50/hour. You only need to stop one (1) customer from leaving for every day of programming this costs. This thread is at +89 and has 32 comments, so it's probably worth at least a programmer-month.

If you can't make your website Firefox compliant in a month, you have some very deep design issues. Firefox compliance is so trivial that most websites achieve it without even trying, because Firefox follows basically the same standards Chrome does.

Yep, but the people making the 'technical' decision to support Firefox only see the gains from reducing the labor.

The loss from not supporting Firefox (which I agree, is probably more than the savings) will show up on somebody else's balance sheet. IT saves a bit of money by siphoning indirectly out of Customer Retention, and the details get lost in the noise. It's the curse of large organizations.

4% of desktop web traffic is Firefox is not at all the same thing as “4% of desktop users also don’t have access to or refuse to use a Chromium based browser and will switch banks because it”.