When using the Responsive Design Mode (in which you can specify the UA; Ctrl + Shift + M) in Firefox, UA is still overwritten by the settings in UserAgent Switcher, i.e. you cannot get mobile views by using this mode if you have specified another UA string in UA Switcher. Yes, I know you can go around by simply switching UA Switcher off or setting it directly to a mobile UA, but it's just a little inconvienent for web developers who just wants to quickly test how the site looks like on mobile UAs.
When using the Responsive Design Mode (in which you can specify the UA; Ctrl + Shift + M) in Firefox, UA is still overwritten by the settings in UserAgent Switcher, i.e. you cannot get mobile views by using this mode if you have specified another UA string in UA Switcher. Yes, I know you can go around by simply switching UA Switcher off or setting it directly to a mobile UA, but it's just a little inconvienent for web developers who just wants to quickly test how the site looks like on mobile UAs.