I'm actually fiddling with the latest Slackware 12.0, featuring XFCE 4.4.1.
One problem I have is that some apps like Firefox, Thunderbird or SeaMonkey use huge fonts compared to my XFCE fonts. Here's a screenshot so you get an idea:
Any idea how I can make these fonts harmonize with XFCE? (E. g. make them smaller so they look like those in the XFCE menus).
So far I found one hint: I opened Firefox, 'about:config' and changed 'layout.css.dpi' from the default -1 to 0.
Problem 1: that only applies to my user, not system-wide.
Problem 2: it only applies to Firefox.
Sorry about your font-size issue in Xfce, and specifically only with Firefox. Here's what I font (ugh!..) you to do:
1. reference this article: http://ubuntuforums.org/showthread.php?t=422350
2. validate that you have consistent dpi (=96) in all display items (Xorg, DMs, etc.)
Hopefully, this will provide some correction...
Mageia 4.1 / Xfce 4.10
"Which is better- Artificial intelligence or REAL stupidity...?"