test: Use MOZ_HEADLESS_WIDTH et al to control Firefox window size
test: Use MOZ_HEADLESS_WIDTH et al to control Firefox window size

The --window-size parameter has no effect.

mvollmer/cockpit,cockpit-project/cockpit,martinpitt/cockpit,mvollmer/cockpit,martinpitt/cockpit,mvollmer/cockpit,mvollmer/cockpit,cockpit-project/cockpit,martinpitt/cockpit,martinpitt/cockpit,cockpit-project/cockpit,cockpit-project/cockpit,mvollmer/cockpit,martinpitt/cockpit,cockpit-project/cockpit