Firefox v47 got pushed to trusty and it causes the selenium web driver to fail completely. Best course of action for now: disable mwext-mw-selenium job.
Firefox 47.0 has been pushed to trusty-updates last week. Its release notes mentions:
Selenium WebDriver may cause Firefox to crash on startup, use Marionette WebDriver instead.
Marionette requires an executable geckodriver which is apparently not packaged in Ubuntu It is a Rust based software available at https://github.com/mozilla/geckodriver/
- get our repository to change their integration env in environments.yaml to explicit use browser: chromium.
- revert back to Firefox 46 and pin it to prevent future updates
Once we get mediawiki_selenium / geckodriver (T137540) we will be able to upgrade.