> is there a way of holding a video- or an audioconference with Firefox (or Vivaldi) on Devuan?  The ones I have come in contact with. such als https://global.gotomeeting.com/,  work only with Windows or Mac and Chrome.

If you have got Devuan, you do not have to resort to browsers for conferencing.

As for audioconferencing or one-to-one video :

qtox or another tox protocol client of your choice is the right tool.

It is also available on most other platforms, for you contacts which are not on *n*x.

/D