explorer verse firefox?

[Vardy]

If my Explorer 11 doesn't support Yahoo Calendar, will Firefox support it?

[Zarn]

That's a false comparison. Whether Internet Explorer 11 does or does not support Yahoo Calendar, doesn't say anything about whether Mozilla Firefox will support it, as there's no inherent connection between the two.

If it doesn't work in your current browser, try another. I'd try Mozilla Firefox. If it didn't work there, I'd try Google Chrome. Each browser is in isolation - at least when they use different rendering engines and code bases, and aren't reskins of one another.