I have a GPD Pocket running Ubuntu 16.04 LTS with Unity and Firefox Quantum. The GPD pocket is a small netbook (7 inch display). For some sites I would therefore prefer seeing on this screen the mobile version of the website (mainly on my work's egroupware server).
How is this possible?
Bonus question (but neither necessary nor sufficient to get the accepted answer): How to do this on Google Chrome/chromium?
I do not care if this is a per website or a global setting as I use different firefox profiles for different things.
###Firefox
Showing the mobile version of websites is a built-in feature in Firefox. In Firefox select Tools -> Web Developer -> Responsive Design Mode and then from the dropdown menu select your device model.
###Chromium/Chrome
Toggle the Device Mode button to turn Device Mode on or off. When Device Mode is on, the icon is blue (). When Device Mode is off, the icon is gray (). Select Tools -> Developer tools -> click Toogle device toolbar button (marked by the mouse cursor in the below screenshot -> click the black downward triangle ▾ to the right of "Responsive" to show the dropdown menu and select your device from the dropdown menu.
You may use an add-on like User-Agent Switcher.
It lets you choose from many options:
(screenshot source: link above)
You can also try substituting m for www in the url or a suitable Firefox addon such as Temporary Mobile View.