I am not sure, but I suspect the browser is going into a program loop. For example: Line 1 = GoTo Line 1

Type about:support in the address bar and press enter.

Under the page logo on the left side, you will see Application Basics. Under this find Profile Folder. To its right press the button Show Folder. This will open your file browser to the current Firefox profile. Now Close Firefox.

Locate the mimeTypes.rdf file. Then rename or delete it. Restart Firefox.

This file tells Firefox what to do with what type of file. The computer system also has a file like this. The wrong entry here could create the loop problem.

Thanks for the quick reply. Unfortunately, this made no difference.

One other possible issue: The failing link is to Office365 (work) and I'm wondering since the URL contains specific account information if there is an issue with the MS Office suite on my computer (not downloaded from that account) vs. the office suite I downloaded to the account owner's PC. In other words, does an attempt to access email online at Office365 try to verify the desktop apps belong to the online account? Even if so, why would IE work and not FireFox?

BTW, the "BACK" list again shows a large number of "Continue" entries.

https://login.microsoftonline.com/login.srf?wa=wsignin1.0&rpsnv=4&ct=1465236757&rver=6.6.6556.0&wp=MBI_SSL&wreply=https%3a%2f%2foutlook.office.com%2fowa%2f%3frealm%3dxxxxxxxxx.com&id=999999&whr=xxxxxxxxx.com&CBCXT=out&msafed=0#wa=wsignin1.0

This is the URL (with domain and ID altered)

It is definitely in a loop as the number of "continues" keep growing.

Sounds like a cookie problem. Could you try:

(1) Make sure cookie settings are liberal for testing purposes. See: Websites say cookies are blocked - Unblock them

(2) Remove existing cookies for microsoftonline.com AND office365.com -- assuming you do not have any unsaved work pending on the system (based on your symptoms, I suspect not). Either:

• right-click (on Mac Ctrl+click) a blank area of the page and choose View Page Info > Security > "View Cookies"
• (menu bar) Tools > Page Info > Security > "View Cookies"
• click the padlock or "i" icon in the address bar, then the ">" button, then More Information, and finally the "View Cookies" button

In the dialog that opens, the current site should be pre-filled in the search box at the top of the dialog. Edit that to microsoftonline.com to list that site's cookies, and then remove them individually. Repeat with office365.com.

Then try logging in again and see whether the redirect is successful.

Oops, in the above reply, please also clear cookies for office.com in addition to office365.com since your "realm" is on that server.

SUCCESS! I just cleared ALL my cookies and it all loaded up just fine.

Thank you so much for the suggestion.