uninstall Firefox. Then Delete the Mozilla Firefox Folders in C:\Program Files and C:\Program Files(x86) Note please do Mac Equivalent Note: your Firefox Profile is saved. But you should make a back up before you do : https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles

https://support.mozilla.org/en-US/kb/export-firefox-bookmarks-to-backup-or-transfer

Reinstall with Current Release Firefox 57.0.2 with a Full Version Installer https://www.mozilla.org/firefox/all/

Please let us know if this solved your issue or if need further assistance.

For https://www.directv.com/

Do you mean the error described in this article: What do the security warning codes mean?

Is that the only site affected?

If you click the "Advanced" button on the error page, could you copy/paste the error info there, especially the SEC_ERROR... code?

The code most commonly raised on the forum is covered by this article: How to troubleshoot security error codes on secure websites.

Does that help or does the mystery only deepen?