I don't have an AT&T account, so I can't test it myself. Is the problem with accessing email? I think AT&T uses Yahoo for its email (the address of your mailbox may be on a Yahoo site). I mention that because Firefox restricts how different servers share cookies and that might be affecting your login.

You could try turn off Tracking Protection for the AT&T site and see whether that makes any difference. At the left end of the address bar, next to the lock icon, click the shield. Then on the drop-down panel, click the slider switch to turn off Tracking Protection on the site and test again. Any difference?

I can login to my yahoo mail account with no problems. It's when I try to login to manage my account that the problem occurs. The page displays redirecting and then switches to AT&T account management/login only to switch back to redirecting. It does this continually. I can switch browsers and login with no problems. I tried turning off tracking and it had no effect.

It's difficult when there's no error message. You could try some of the usual things:

If a site is generally known to work in Firefox, these are standard suggestions to try when it stops working normally:

Cache and Cookies: When you have a problem with one particular site, a good "first thing to try" is clearing your Firefox cache and deleting your saved cookies for the site.

(1) Clear Firefox's Cache

See: How to clear the Firefox cache (only select Cached web content, don't clear all cookies and site data)

If you have a large hard drive, this might take a few minutes.

(2) Remove the site's cookies (save any pending work first). While viewing a page on the site, click the lock icon at the left end of the address bar. After a moment, a "Clear Cookies and Site Data" button should appear at the bottom. Go ahead and click that. Firefox will ask you to confirm; go ahead and confirm.

Then try reloading the page. Does that help?

Double-check content blockers: Firefox's Tracking Protection feature, and extensions that counter ads and tracking, may break websites that embed third party content (meaning, from a secondary server).

(A) [Already Done] The shield icon toward the left end of the address bar usually turns a bit purplish when content is blocked. Click the icon to learn more or make an exception. See: Enhanced Tracking Protection in Firefox for desktop.

(B) Extensions such as Adblock Plus, Blur, Disconnect, DuckDuckGo Privacy Essentials, Ghostery, NoScript, Privacy Badger, uBlock Origin or uMatrix may block required elements on a site. Usually you can find a toolbar button for each add-on to manage blocked content in a page. There may or may not be a number on the icon indicating the number of blocked items; you sometimes need to click the button to see what's going on and test whether you need to make an exception for this site.

Testing in Firefox's Troubleshoot Mode: In this mode, Firefox temporarily deactivates extensions, hardware acceleration, any userChrome.css/userContent.css files, and some other advanced features to help you assess whether these are causing the problem.

If Firefox is running:

You can restart Firefox in Troubleshoot Mode using either:

• "3-bar" menu button > Help > Troubleshoot Mode... (before Fx88: Restart with Add-ons Disabled)
• (menu bar) Help menu > Troubleshoot Mode... (before Fx88: Restart with Add-ons Disabled)

and OK the restart. A small dialog should appear. Click the Open button (before Fx88: "Start in Safe Mode" button).

If Firefox is not running:

Hold down the Shift key when starting Firefox. (On Mac, hold down the option/alt key instead of the Shift key.) A small dialog should appear. Click the Open button (before Fx88: "Start in Safe Mode" button).

Note: Don't use the Refresh without first reviewing this article to understand what will be deleted: Refresh Firefox - reset add-ons and settings.

Any improvement?

It was the Adblock extension. Thanks for your help.