You can check the Web Console (Tools -> Web Developer) for error messages about blocked and unsafe and mixed content.

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

If you use extensions ("3-bar" menu button or Tools -> Add-ons -> Extensions) that can block (wanted) content (e.g. Adblock Plus, NoScript, Ghostery, uBlock Origin) always make sure such extensions do not block (wanted) content.

• make sure your extensions and filters are updated to the latest version

You can try these steps in case of issues with web pages:

You can reload web page(s) and bypass the cache to refresh possibly outdated or corrupted files.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 the cookies from websites that cause problems via the "3-bar" Firefox menu button (Options/Preferences).

"Clear the cache":

• Options/Preferences -> Advanced -> Network -> Cached Web Content: "Clear Now"

"Remove the cookies" from websites that cause problems.

• Options/Preferences -> Privacy -> "Use custom settings for history" -> Cookies: "Show Cookies"

Start Firefox in Safe Mode to check if one of the extensions ("3-bar" menu button or Tools -> Add-ons -> Extensions) or if hardware acceleration is causing the problem.

• switch to the DEFAULT theme: "3-bar" menu button or Tools -> Add-ons -> Appearance
• do NOT click the "Refresh Firefox" button on the Safe Mode start window

• https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode
• https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems

Thanks, Ive found out what the problem is

The content was blocked "because tracking protection is enabled" If I turn it off, then it displays. There was also something about mime?

So now the problem is, how do I have tracking protection enabled, but display the content? I cant find anywhere to add the website or email address to an allowed list?

L_C123 said

So now the problem is, how do I have tracking protection enabled, but display the content? I cant find anywhere to add the website or email address to an allowed list?

Would you please try this :

3-bar menu (or 'Tools') => Privacy => under 'Tracking' : 'Change Block List'

In case this is just about the images not loading, you could also check this :

Click on the little 'i' in a circle on the left side of the address bar, then click on the little black arrow and then on 'More Information'. Under the Persmissions tab : scroll down till you find 'Load Images' and set it to 'Allow'.

Any good  ?

When I clicko n change block list, there are only 2 options. Its set at the recommended one - disconnect.me basic protection. Theres no option to add an email address or website?

If I set images to allow they still dont load.

But if I click on the "i" then disable tracking protection, they load. But I cant find anyway to allow tracking from just this email address?

Embdedded content / images load in other emails I get, but not in others. So Im guessing the ones it loads for arent tracked?

Maybe this article will be helpful :

Tracking Protection in Private Browsing

Would you also take a look at this please :

https://support.mozilla.org/en-US/kb/fix-problems-images-not-show#w_check-image-permissions-for-a-specific-website

Do you have any security or anti-virus software installed  ? If so, would you disable it (for now) to see if that will make a difference  ?

Think the easiest way is going to be just disable tracking protection for these emails, read the email and then enable it again!

Thanks for your help