You can open the Web Console (Tools > Web Developer). Check on the Network tab to see if you can identify what content is causing this delay.

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

You can reload web page(s) and bypass the cache to refresh possibly outdated or corrupted files.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
• Press "Ctrl + F5" or press "Ctrl + Shift + R" (Windows,Linux)
• Press "Command + Shift + R" (Mac)

Clear the cache and remove cookies only from websites that cause problems.

"Clear the Cache":

• Firefox > Preferences > Advanced > Network > Cached Web Content: "Clear Now"

"Remove Cookies" from sites causing problems:

• Firefox > Preferences > Privacy > "Use custom settings for history" > Cookies: "Show Cookies"

Start Firefox in Safe Mode to check if one of the extensions (Firefox/Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem.

• Switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance
• Do NOT click the Reset button on the Safe Mode start window

• https://support.mozilla.org/kb/Safe+Mode
• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

Try to disable IPv6 (check for other possible causes as well).

• http://kb.mozillazine.org/Error_loading_websites

Unfortunately I've tried all of these things already. I have also confirmed across several machines and tried a 'private window'.

Thanks. Any other ideas?

Actually, IPv6 toggle seemed to have helped. My problem is that everyone on a Mac in FF is experiencing the same issue. So is this a host problem? I can't expect all by visitors to toggle that FF setting.