Apparently this site uses "suspicious cross-site POST requests" according to NoScript in Firefox.
Until this changes, you'll need to tweak the NoScript settings a little in order to be able to sign into your community.vzw.com account with NoScript XSS sanitizing enabled. (I'll assume you've already allowed scripts from vzw.com and/or lithium.com - I'm pretty sure you'll need those enabled in order to use the forums at all)
For the past two days I've been trying to get my community.vzw.com account setup and running and no matter what I tried, I would always end up on a screen that said my user name and password was invalid. To add to the confusion I was able to reset my password on the account using the "Forgot username/password" link and it STILL wouldn't work.
Then I noticed that for a split second right after I press the enter key to login there is a small notification bar at the top of the browser window. It goes away too fast to read, but I was able to notice the "NoScript" icon on the bar before it disappeared. So, I enabled scripts globally in NoScript and STILL had the same problem. Disabling/Removing NoScript all together fixed the problem and I was able to login. Of course that's not an acceptable solution, but at least I knew for sure that the problem was being caused by NoScript now.
Recalling past situations with sites not playing well with NoScript I remembered that there were NoScript messages logged in the Firefox error console (Tools -> Error console) when some actions are blocked. So, I enabled NoScript again, tried to login, opened the error console and sure enough, there's a message saying:
So, I took the URL from the "to ..." section of the message and entered it into the equivalent regular expression into the exceptions and tada! It worked! I can now sign into the community forums and still have the protection of NoScript to keep me safe from other sites.
Thanks for the expert advice. Adding the line to the Anti-XSS exception worked for me. I still can't use my forum name and password to log in but at least I can use my verizon.com one without first going through the main page.