That makes no sense? What money needs to be invested?
If you're talking about an intranet website, then yeah, it costs money to develop it to work in both IE and FF...though, I'd argue, it's simpler just to code to the standard and it shouldn't require more than a minimal amount of work to make it work in all browsers.
Second, if you're talking about a company's internet presence, they lose money not catering to the majority of browsers. If I want to buy something, and your site doesn't work in FF, I go elsewhere. I don't even check to see if it works in IE...it might, but it's not worth my time, I'll go to one of your competitors.
Third...if you're referring to installing FF so your staff can use it, that doesn't cost money, just don't install it. But don't stop staff who want to use it from using it.
I don't see this "cost" you're talking about.