You can reload web page(s) and bypass the cache to refresh possibly outdated or corrupted files.

• Hold down the Shift key and left-click the Reload button              <I used this one after clearing history &cookies did not work on firefox and then it worked ok...
  
• Press "Ctrl + F5" or press "Ctrl + Shift + R" (Windows,Linux)
• Press "Command + Shift + R" (Mac)

You can open the Web Console (Firefox/Tools > Web Developer).Check on the Network tab if any content is blocked and has a file size 0 (zero).

• https://developer.mozilla.org/Tools/Web_Console

You can also check the web Console log for (JavaScript) errors.
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I have done EVERYTHING imaginable in the last several days ATTEMPTING to return to normalcy in using this site.  Clearing history, clearing cookies, clearing saved passwords, running Norton 360, restarting my computer, reloading Firefox (I thought).  Absolutely NOTHING would resolve my ability to log-on as a Forum participant! 

Specifically,
- I could not get past the 'spinning wheel' using Firefox.
- I could read the Forum entries using Internet Explores, but could not log-in as a participant.

Your direction to toggle the 'Y-Blocks Forever' web site on my PC and then press "Ctrl + F5" (F5 is a key in the top on my keyboard) INSTANTLY resolved my Firefox webpage contents so that log-in was again visible AND access to viewing Forum topics and threads was doable using Firefox.

Thanks, again, tomfiii!