Here we go, again.

In the wee small hours of Friday morning I did, yet, again, another fresh install of Slackware64-current. Other than installing LibreOffice, VLC, flash, java and Pale Moon, nothing has been changed.
Xfce has become my desktop of choice, but an hour or so ago I switched over to kde-4, and, once again, the fonts in Firefox
and Thunderbird are so small as to make both packages nearly
unusable.
Oxygen-gtk2 is installed as is the latest font and theme
changer for the two programs in question.
Nothing works, the fonts for the panels, menus, etc., in Firefox and Thunderbird cannot be changed.
Has anyone solved this problem?
Thanks.

Have you tried to CTRL+Scroll up?

Or

CTRL++

That won't do a thing for the fonts in the toolbars, panels, or menus.

Check what font size is set in gtkrc (2.0) and gtkrc (3.0) and there used to be also gtkrc-kde I think it was called.
And there is qtconfig (4.x) and qt5ct (5.x) which can set font size regardless of what is set in systemsettings.

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How about ~/.config/gtk-3.0/settings.ini

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Yeah, how about ~/.config/fontconfig/fonts.conf and ~/.config/Trolltech.conf

Everyone got their own standard. It reminds me why I got rid of KDE and GTK+3

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A big "thank you" to everyone for their suggestions.

Going back to Xfce is the quickest fix but that doesn't solve the problem for kde4 users, so I will try the ideas posted above.

BTW, earlier in the week I tried, again, kde5 and I don't see any benefit(s) to be gained. Until kde5 can peacefully co-exist with Xfce I won't be installing it again and won't install it, if and when, it replaces kde4 in -current.

cwizardone - do you have custom font settings in Firefox and Thunderbird? Try resetting DPI settings to "system" instead of a custom dpi value, if you are using that.

From what you read, your Plasma5 experience is no different than the current KDE4 in that both cause your fonts to shrink in Mozilla products.
If this was a generic bug I assume that we would have seen many more posts about it, so it is quite probably that the issue you experience is somehow caused by your customizations.

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Thank you for your reply.
I have tried your suggestion, but, sorry, it doesn't change a thing. The fonts in the panels, menus, toolbars, etc. are still too small, unless, of course, a user puts his nose up to the screen.

Well, just to be thorough, I renamed the .kde directory and started a 'fresh' kde session.
Long story short, it didn't make a bit of difference. The fonts for the firefox/thunderbird toolbars, panels, etc., are too small and cannot be changed.


Back to Xfce.

I've looked around, and found a thread where source says:

This was 2 years ago, not sure what happened after that.

So I guess it means you'll have to write some CSS wherever GTK+3 loads CSS from, and find out the names of these menus and panels if you want to define font size for each of them.

Something like this would probably work for all fonts :

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Just out of curiosity, what kind of monitor are you using cwizardone?

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A fairly recent 1920x1080 LED/LCD monitor.

X11 DPI setting, perhaps?

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What login manager are you using? Perhaps the ServerArgsLocal option in /etc/kde/kdm/kdmrc can help here, if you pass "-dpi 96" to it, for example.

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