const PAGE = "data:text/html,page"; function test_on_browser(browser) { ok(!browser.audioMuted, "Audio should not be muted by default"); browser.mute(); ok(browser.audioMuted, "Audio should be muted now"); browser.unmute(); ok(!browser.audioMuted, "Audio should be unmuted now"); } add_task(async function () { await BrowserTestUtils.withNewTab( { gBrowser, url: PAGE, }, test_on_browser ); });