Click on menu icon on right (3 lines icon), choose preferences -> language and appearance -> alongside the font line, click the 'advanced button' and make sure 'allow pages to choose their own fonts' is ticked.

Nicely done Fred. It took me a bit to figure out the problem was with Firefox, and then come up with poor guesses and poor advice on searches. I figured this community would know and I'm relieved someone here did. Thanks.

Your welcome, I'm glad its sorted for you ;)