Added this to the Wiki list of useful Xfce Commands.You can always test theme issues by using the default Adwaita theme. To test firefox with the default GTK3 theme (adwaita), first close firefox then start it with:
GTK_THEME=Adwaita firefox
Test theme for GTK3
Test theme for GTK3
With MX-17 and its Stretch base ahead, I thought this from ToZ on the Xfce Forum might be useful:
Production: 5.10, MX-23 Xfce, AMD FX-4130 Quad-Core, GeForce GT 630/PCIe/SSE2, 16 GB, SSD 120 GB, Data 1TB
Personal: Lenovo X1 Carbon with MX-23 Fluxbox and Windows 10
Other: Raspberry Pi 5 with MX-23 Xfce Raspberry Pi Respin
Personal: Lenovo X1 Carbon with MX-23 Fluxbox and Windows 10
Other: Raspberry Pi 5 with MX-23 Xfce Raspberry Pi Respin