Context:

• Playwright Version: 1.7.0
• Operating System: Linux, Heroku
• Node.js version: v12.20.0
• Browser: Firefox

Code Snippet

// @ts-check
const playwright = require("playwright");

(async () => {
    const browser = await playwright.firefox.launch();
    const context = await browser.newContext();
    const page = await context.newPage();
    await page.goto('http://whatsmyuseragent.org/');
    await page.screenshot({ path: `example.png` });
    await browser.close();
})();

Describe the bug

Firefox can't start, the tab suprocess crashes. It was working with 1.5.1 but with 1.7.0 I run into this weird error (not me actually, I'm maintaining the Heroku buildpack, probably then the users).

The full logs see here:
log (1).txt

GLib-GObject-CRITICAL **: 18:20:18.805: g_signal_connect_data: assertion 'G_TYPE_CHECK_INSTANCE (instance)' failed

Related PR: playwright-community/heroku-playwright-example#8