This can happen when Firefox has a problem to access locally installed fonts because of sandbox security issues. https://wiki.mozilla.org/Security/Sandbox

You can set this pref to 2 or 1 on the about:config page to lower the sandbox security setting.

security.sandbox.content.level = 1

Close and restart Firefox to make the change effective.

If '1' still doesn't have an effect then try '0' to disable the sandbox.

If this didn't work then undo/reverse the change and reset the pref via the right-click context menu to the default value.

Type about:config<enter> in the address bar. If a warning screen comes up, press the I Accept the Risk button. At the top of the screen is a search bar.

thank you very much, took me a while to find where & what but did it, stoked!!!! thanks, Craig

This problem is supposed to be fixed on Mac OS X 10.11 and earlier with Firefox 60.0.2 according to the Release Notes.

• https://www.mozilla.org/en-US/firefox/60.0.2/releasenotes/

What font manager are you using?

See comment 44:

• bug 1460917#c44 - Fonts not displaying with OS X 10.11 and Earlier with Font Managers

CraigDawick said

took me a while to find where & what but did it, stoked!!!!
thanks, Craig

Glad to help. Safe Surfing.