Yahoo uses a lot of different servers to host email. Currently mine is on us-mg4.mail.yahoo.com. I don't think end-users have any control over that. I'm surprised that IE is showing you a different URL for the same mailbox.

When I use IE I get this: https://login.yahoo.com. With FF I get what I said in my original question.

My concern is that with Yahoo mail with FF when I click on "Inbox" or any other folder I get a visual "flash" like the request is starting, but nothing happens. I have to click "refresh" in the address bar, to see my e-mails.
I  do not know my e-mail server is. My ISP is Charter cable, but why is this not both browsers?
Thanks for the reply.
Bob

hello, as a first troubleshooting step please try to clear the cache & cookies from yahoo.com and reload the page.

if the problem is still there afterwards you could try to replicate this behaviour when you launch firefox in safe mode once? if not, maybe an addon is interfering here...

Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems

I suspect in IE, once you log in, you will go to a similar looking domain. Perhaps you are saving a cookie that logs you in in Firefox, or using a saved password. Either way, Philipp's advice should help with the functional issues.

I had cleared the cache earlier, and I started FF in the Safe Mode, but the URL in the address bar stayed the same.

But,  now I don't seem to have the problem I had earlier opening the Inbox and other folders.
I do not have any Add Ons in my FF.
Thank you both for your suggestions. I'll see what happens as time goes by.
Bob

Here is what is happening now with FF and Yahoo mail.I have two Yahoo e-mail accounts, and they act the same.

When I open my Yahoo e-mail page and click on "Inbox" or any other folder nothing happens. But, if I refresh the page the "Inbox" opens. Another thing I noticed: When I open the e-mail page my cursor is the "arrow". If I click on an e-mail, or anything else, I am directed to a spam web site,but if I refresh the page the "hand" cursor appears, and I am able to access my e-mails like I am supposed to. The only way to get the "hand" cursor is to refresh the page.
To be honest the "us-mg5-mail.yahoo.com" may have been there all the time, and I just didn't pay attention to it.
But, also this happens only in FF. When I use IE my Yahoo e-mail works.
Could it be Yahoo's fault? But if it was IE would have the problem as well as FF.
Bob

Another thing I just noticed.The cursor problem I mentioned in my previous post also happens in my Yahoo Groups when I use FF.

Bob

Spam redirection is very troubling. Could you double-check for possible extensions on this tab:

orange Firefox button (or Tools menu) > Add-ons > Extensions category

If you find anything there, disable it and then restart Firefox to see whether the behavior changes.