test: Fix preferences for new Firefox
test: Fix preferences for new Firefox

We need to use firefox nightly since shipped versions don't include
`--remote-debugging-port` option. For this we want to disable automatic
updates.

Also we need `remote.frames.enabled` due to https://bugzilla.mozilla.org/show_bug.cgi?id=1593226

Closes #14192
cockpit-project/cockpit,mvollmer/cockpit,deryni/cockpit,garrett/cockpit,deryni/cockpit,cockpit-project/cockpit,deryni/cockpit,martinpitt/cockpit,garrett/cockpit,deryni/cockpit,cockpit-project/cockpit,martinpitt/cockpit,mvollmer/cockpit,garrett/cockpit,mvollmer/cockpit,martinpitt/cockpit,deryni/cockpit,moraleslazaro/cockpit,cockpit-project/cockpit,garrett/cockpit,deryni/cockpit,moraleslazaro/cockpit,garrett/cockpit,mvollmer/cockpit,cockpit-project/cockpit,martinpitt/cockpit,moraleslazaro/cockpit,moraleslazaro/cockpit,moraleslazaro/cockpit,mvollmer/cockpit,martinpitt/cockpit,moraleslazaro/cockpit,moraleslazaro/cockpit,deryni/cockpit