fix: check if installed FF supports use-cached

bench/utils/bench.py

@@ -354,11 +354,17 @@ def build_assets(bench_path=".", app=None, using_cached=False):
 	if app:
 		command += f" --app {app}"
 
-	if using_cached:
+	if using_cached and can_use_cached(bench_path):
 		command += " --using-cached"
 
 	exec_cmd(command, cwd=bench_path, env={"BENCH_DEVELOPER": "1"})
 
+def can_use_cached(bench_path=".") -> bool:
+	cmd = ["bench", "can-use-cached"]
+	return_code = subprocess.call(
+		cmd, cwd=bench_path, stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL,
+	)
+	return not return_code
 
 def handle_version_upgrade(version_upgrade, bench_path, force, reset, conf):
 	from bench.utils import log, pause_exec