>>      I built it on Devuan Jessie without any glitch and Skype seems happy
>> with it.

> Would you post contents of Firefox?:
>    about:config > security.sandbox.content.write_path_whitelist

     I built Apulse on a Devuan-Jessie x86_64 without Pulseaudio. This 
was for Skype to install without error. It was happy at installation but 
the microphone does not work. One of the machines on which it is 
installed is a desktop without a microphone therefore this isn't a 
software issue, but the other is a laptop with a microphone. Your mail 
reminds me that Pulseaudio "clients" need to be launched in a special 
way for Apulse to play its role, and there is a script for that, 
/usr/local/bin/apulse

     Therefore the command in skypeforlinux.desktop should be changed from
Exec=/usr/bin/skypeforlinux %U
     to
Exec=/usr/local/bin/apulse /usr/bin/skypeforlinux %U

     And this should be done for all Pulseaudio "clients". I will try to 
launch Skype like this as soon as possible on the laptop.

     The preferred browser on the two machines is Palemoon, installed 
from some Suze repository. There is also Firefox installed and it works 
with Alsa only, since it is always launched from the standard .desktop 
launcher. Maybe I should check if the version of FF is the last one and 
check it still works. I will also try to launch it with pulseaudio.

         AFAIU, the only thing the script is doing is to include 
/usr/local/lib/apulse in LD_LIBRARY_PATH; therefore it should be enough 
to add a a proper file apulse.conf in /etc/ld.so.conf.d and run 
ldconfig. And then the standard .desktop files could be used.

     Didier