firefox: fix build

5 jobs for master in 74 minutes and 1 second (queued for 3 seconds)
Status Job ID Name Coverage
  Package
passed #10168
PKGBUILD
build_pkgs

01:11:30

failed #10164
PKGBUILD
build_pkgs

00:06:24

 
  Sign
passed #10165
signature
sign_pkgs

00:00:44

 
  Deploy
passed #10166
rsync allowed to fail manual
deploy_pkgs

00:00:47

 
  Stable
passed #10167
rsync allowed to fail manual
move_pkgs_to_stable

00:00:58