In mobile versions of browsers, in the menu, there is an option computer mode, why not make the computer version of Firefox, mobile mode?To test sites.
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This feature already exists. It is called responsive design mode and is part of the developer tools.
https://firefox-source-docs.mozilla.org/devtools-user/responsive_design_mode/
@Nich, is that what you're looking for? (Check out @KevinBrosnan's comment in this thread)
Just want to make sure before updating status.
never-displayed