I'm not particularly experienced with web browsers, but whenever I hear people who know what they're talking about, I always leave convinced that this is exactly the problem.
If there are sites that work on Chrome but not Firefox, it just seems to me that either:
- Chrome or Firefox must be breaking web standards
- Web standards must be unspecified for that use case
I have no idea the fix though, the web is so massively complex now, that I don't even know what specifying standards for every use case would involve.