ci: take firefox back a bit for more speed

4 jobs for split_server_and_client in 7 minutes and 44 seconds (queued for 3 seconds)
Status Name Job ID Coverage
  Build
passed build #56060

00:05:14

 
  Test
passed lint #56063

00:00:18

passed test:chrome #56061

00:01:01

passed test:firefox #56062

00:01:10