Earlier quoted context omitted.
It's IE all over again. Sometimes you can't.
If you have those one or two very specific websites that just cannot cope with Firefox, just use Chrome for them. They're likely not the ad-filled pages anyway, but rather some specific companies. We've done this for the IE in the past, we can do it today. It really doesn't take that much time. There's only one thing that will fix this situation long term and it's lowering chrome's market share. Don't stick with it a…
Most of those "cannot copes" can be fixed by changing the user agent to that of Chrome. Most sites that refuse to work in other browsers simply don't test on anything but Chrome and don't want the support burden.