The solution does not work anymore.
It seems this time there was no update to freetype.
The font anti aliasing in the manjaro settings is deactivated.
The fonts in the manjaro settings manager is also rendered without the truetype/subpixel. Same for Libeoffice which looks fine.
The title bar of these 3 example tools is rendered correctly without truetype/subpixel. But the bookmark bar and the webpage content has this rendering active.
Does anything changed in manjaro on how the font rendering is handled?
I was able to find the solution for Firefox on my own
Because Firefox seems to ignore the Xfce settings or something, I edit the global one and this one is used by Firefox for Menu and web page rendering.
Firefox seems to ignore $HOME/.config/fontconfig/fonts.conf as well.