Comment # 5 on bug 1125078 from Thomas H�nig

I can confirm the behaviour for XFCE (and the dependency from fontconfig) too 

After installing snapshot 20190209 Firefox became unuseable. Stumbling over 

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=909818
and
https://www.preining.info/blog/2018/10/firefox-got-maniac/

I rebuilt 
fontconfig-2.12.6-2.4.x86_64
and 
fontconfig-32bit-2.12.6-2.4.x86_64

from another (older) installation and with those applied everything went back
to normal.