Walt said

On new mail, the icons for contacts, calendar etc do not display

Hello Walt,

Your system details show that you have this extension installed :

https://addons.mozilla.org/en-US/firefox/addon/yahoomailhideadpanel/

In the reviews I see someone mention that the icons for contacts etc. disappeared ....

Assuming that your problem is with Yahoo Mail (why else would you have that extension ?); would you (just for now) disable the extension and see if the icons re-appear ?

Special icon are usually supplied by a icon font that is downloaded from internet. If you do not see the icons then make sure you do not block these icon files.

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

• make sure your extensions and filters are updated to the latest version
• https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems

Firefox shows an highlighted shield icon at the left end of the location/address bar in case Tracking Protection is blocking content.

• click the shield icon for more details and possibly disable the protection

You can check in the Web Console what content is blocked.

• "3-bar" menu button or Tools -> Web Developer
• https://support.mozilla.org/en-US/kb/enhanced-tracking-protection-firefox-desktop