You could try the site in Firefox's Safe Mode to rule out potential blocking by ALL of your extensions. That's a standard diagnostic tool to deactivate extensions and some advanced features of Firefox. More info: Diagnose Firefox issues using Troubleshoot Mode.

You can restart Firefox in Safe Mode using either:

• "3-bar" menu button > "?" button > Restart with Add-ons Disabled
• Help menu > Restart with Add-ons Disabled

Not all add-ons are disabled: Flash and other plugins still run

After Firefox shuts down, a small dialog should appear. Click "Start in Safe Mode" (not Reset).

Any difference?

Thanks. There was no change. I only use 5 add ons and the non-Adblock Plus ones would be unlikely culprits anyway. I don't even see placeholders for the ads from this site. Once, while trying to whitelist this site, I did see some Flash in a banner ad on one page, but that change did not persist.

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

Thanks. Every file listed under the Network tab has a positive size.

Are you forcing the site to a secure connection? It's possible in that case that the way ads are embedded is triggering a mixed content block. Typically you would see a "shield" icon at the left of the address in that case.

Edit: Or maybe the site doesn't show ads when you use HTTPS because it assumes you are logged in?

It looks like this is not a Firefox problem after all. Occasionally in FF I do see some Flash and I just noticed that Chrome is also displaying ads from this site erratically.

Thanks for the help.

It is a secure connection but I don't see a shield icon. The site does distinguish between types of memberships though. My membership is supposed to see ads. Right now, I am able to see some Flash in FF and Chrome. Other content is being displayed erratically in Chrome. For example, in Chrome, I clicked on an entirely blank area and the ad in that area, as well as the banner, suddenly became visible. However, that trick hasn't worked again.

IE -- yes, it came to that -- seems to show almost all of the ads but, like Chrome, there is a lot of flickering in the placeholders before the images are finally loaded.