Many site issues can be caused by corrupt cookies or cache.

• Clear the Cache and

• Remove Cookies
  Warning ! ! This will log you out of sites you're logged in to.

Type about:preferences<Enter> in the address bar.

• Cookies; Select Privacy. Under History, select Firefox will Use Custom Settings. Press the button on the right side called Show Cookies. Use the search bar to look for the site. Note; There may be more than one entry. Remove All of them.
• Cache; Select Advanced > Network. Across from Cached Web Content, Press Clear Now.

If there is still a problem, Start Firefox in Safe Mode {web link} A small dialog should appear. Click Start In Safe Mode (not Refresh). While you are in safe mode;

Type about:preferences#advanced<Enter> in the address bar.

Under Advanced, Select General. Look for and turn off Use Hardware Acceleration.

Poke around safe websites. Are there any problems?

Then restart.

You indirectly resolved the problem. I have all history, cookies and cache cleared when I close firefox. Your directions got me to the general area of where I had those settings, but I couldn't find them until I disabled private browsing mode which had somehow become enabled.

Tools/Options/Privacy/

ATT appears fine.

Thanks

Yes, private browsing windows use Tracking Protection, and for some reason that renders the AT&T site blank. If you want to keep using private browsing, you can make one-time exceptions to tracking protection, or turn the feature off under Privacy Options. More info: What happened to Tracking Protection?.

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