Don't work in responsive mode with the mouse :(
Describe the solution you'd like I would like this work in responsive mode with the mouse
Hi! Sorry the late, I'm a little bit confused about the exact issue, it works totally fine on responsive mode with the devtools for me, if what you are wondering is if this can work with the device type option set to mobile well, that's a whole other story, for now the extension will only work with desktop mode but no mobile emulation mode, if this is the case I'll need to check if this is a wanted functionality as I need to calculate effort to develop it.

Hi, yes the issue is related with mobile option, for the moment I use shutter http://shutter-project.org/, but it will be cool that page-ruler work in mobile mode ;)
There is no Desktop mode any more, responsive always assumes mobile, so is not usable if you need to resize.