This is on 2 different hardware systems installed form most recent ISO # 2385 and fully updated.
First I tend to want a bit larger type font than the default. So I set this in SystemSettings5 both under Appearance>Fonts and Appearance>Application Style (for GTK apps). However in Firefox and Thunderbird I have the relatively tiny default font not what I set. Thus settings in SystemSettings5 appear to be not respected by the system for these GTK apps.
To make things more confusing for me in an older installation (on my desktop) from I think ISO #2348 but fully updated the fonts in FF and T-Bird are what I expect and what I set. How can this be?
What or where should I be looking to track down what is causing this? Any ideas why this occurs?