Hi methnerg , It is possible that you have a corrupt cookie or cache for the verizon site. Try this first:

1. Go to about:permissions in a new window
2. Search for the verizon site
3. Click "Forget this site" and restart Firefox

This will remove all cookies, history and cache contents for this site in your profile, as if you were visiting it for the first time on this computer. Try to login again. If it continues, temporarily use another browser and check with Verizon support.

Java Downloads for All Operating Systems

Make sure your Java (Not JavaScript) is up to date Verify Java and Find Out-of-Date Versions {web link}

Version 8 Update 40

Note that "Forget About This Site" will remove all data stored in Firefox from that domain like bookmarks, cookies, passwords, cache, history, and exceptions, so be cautious and if you have a password or other data from that domain that you do not want to lose then make sure to backup this data or make a note.

You can't recover from this 'forget' unless you have a backup of the involved files.

It doesn't have any lasting effect, so if you revisit such a 'forgotten' website then data from that website will be saved once again.