[lewisl9029]

Vertical tabs in Edge seems to trigger false positives on this. Really hope that's not the only heuristic they're using.

[ajot]

Same goes for Sidebery in Firefox, but then it changes to "no" if I do open the Dev Tools. As a non web-dev, this behaviour is truly weird.

[sli]

Looking at the code[0], it just defines an aspect ratio threshold (170px in either direction, on line 13) for your browser's viewport and triggers if it's outside of that on width or height. So when you open a second panel, your viewport goes back to being closer to 16:9/16:10 and the tool considers that within both thresholds.

The detection is hilariously primitive, entirely unreliable, and only knows about your devtools directly if you're using Firebug.

[0]: https://github.com/sindresorhus/devtools-detect/blob/main/in...