Add an overriden Firefox desktop file to make it work right after installation

2 jobs for master in 6 minutes and 29 seconds (queued for 1 second)
Status Job ID Name Coverage
  Package
passed #277928
librem5
build-debian-package

00:01:50

 
  Test Package
passed #277929
librem5
autopkgtest-debian-package

00:04:38