Karma tests using Firefox in VisualEditor/VisualEditor repo are failing. The same tests in Chrome finish successfully.
Example: https://gerrit.wikimedia.org/r/c/VisualEditor/VisualEditor/+/619033
Log: https://integration.wikimedia.org/ci/job/visualeditor-node10-browser-docker/1597/console
22:21:47 Running "karma:firefox" (karma) task 22:21:47 07 08 2020 20:21:47.251:WARN [filelist]: All files matched by "/src/node_modules/qunit/qunit/qunit.js" were excluded or matched by prior matchers. 22:21:47 07 08 2020 20:21:47.349:INFO [karma-server]: Karma v5.0.9 server started at http://0.0.0.0:9876/ 22:21:47 07 08 2020 20:21:47.350:INFO [launcher]: Launching browsers FirefoxHeadless with concurrency unlimited 22:21:47 07 08 2020 20:21:47.351:INFO [launcher]: Starting browser FirefoxHeadless 22:22:47 07 08 2020 20:22:47.352:WARN [launcher]: FirefoxHeadless have not captured in 60000 ms, killing. 22:22:47 07 08 2020 20:22:47.449:INFO [launcher]: Trying to start FirefoxHeadless again (1/2). 22:23:47 07 08 2020 20:23:47.468:WARN [launcher]: FirefoxHeadless have not captured in 60000 ms, killing. 22:23:47 07 08 2020 20:23:47.573:INFO [launcher]: Trying to start FirefoxHeadless again (2/2). 22:24:47 07 08 2020 20:24:47.592:WARN [launcher]: FirefoxHeadless have not captured in 60000 ms, killing. 22:24:47 07 08 2020 20:24:47.717:ERROR [launcher]: FirefoxHeadless failed 2 times (timeout). Giving up. 22:24:47 Warning: Task "karma:firefox" failed. Use --force to continue.
This started happening today after 15:00 UTC, the last change that passed CI was https://gerrit.wikimedia.org/r/c/VisualEditor/VisualEditor/+/618778.