bookmark-audio-fragment/app/scripts

async function onHeadersReceived({ responseHeaders, url, tabId }) {
	const isAudio = responseHeaders.some(header =>
		header.name === 'Content-Type' && header.value.startsWith('audio/')
	);

	if (isAudio) {
		browser.tabs.executeScript(tabId, {
			runAt: 'document_end',
			file: '/scripts/contentscript.js',
		});
		browser.tabs.insertCSS(tabId, {
			runAt: 'document_end',
			file: '/assets/main.css',
		});
		browser.tabs.insertCSS(tabId, {
			runAt: 'document_end',
			file: '/assets/waveform-playlist.css',
		});
	}
}

browser.webRequest.onHeadersReceived.addListener(
	onHeadersReceived,
	{
		urls: ['<all_urls>'],
		types: ['main_frame'],
	},
	['responseHeaders'],
);