Lighthouse resets emulation incorrectly after DevTools run

FAQ

• Yes, my issue is not about variability or throttling.
• Yes, my issue is not about a specific accessibility audit (file with axe-core instead).

URL

https://1uqxj0.csb.app/

What happened?

Lighthouse seems to reset the screen width emulation on mobile devices (from window.screen.width) after a report is generated. This can affect subsequent reports.

To reproduce:

1. Open the URL on Chrome, using responsive mode change your device to any device with < 600px width (e.g. iPhone SE).
2. Refresh the page – you should see the page display the text “portrait”.
3. Run a Lighthouse report. While the test is running, the page should also display “portrait”.
4. Once page refreshes after the report is generated, the page will display “landscape”. Refreshing the page will still show “landscape”.
5. Any subsequent runs of Lighthouse will also display “landscape” on the screen.

You can reset this by going out of responsive mode and going back in.

What did you expect?

I expected Lighthouse to maintain the window.screen emulation after the first report.

What have you tried?

Running without Lighthouse works fine – you can jump in and out of responsive mode without any hitches. Firefox and Safari also work fine.

How were you running Lighthouse?

Chrome DevTools

Lighthouse Version

9.5.0

Chrome Version

102.0.5005.61

Node Version

No response

OS

MacOS

Relevant log output

No response

[adamraine]

The workaround for DevTools will land in M105. This still affects things like user flows so I’m gonna leave the issue open.

Maybe there is a workaround but hopefully there is a proper CDP solution.

[sidvir]

Thanks so much for the quick response! When can I expect the lighthouse fix/workaround to hit Chrome?