That particular site doesn't seem to have a mobile version, I tried loading it with both a desktop and mobile useragent string and there was no difference that I could see.

You can set a default useragent string to view ALL sites in mobile mode if available by typing in about:config then click the plus sign to add a new value.

Add general.useragent.override to the NAME field. Change the type from BOOLEAN to STRING. Add Mozilla/5.0 (Android 4.4.2; rv:42.0) Gecko/42.0 Firefox/45.0.1 to the STRING field.

This will tell every site you visit that you want to view it in mobile mode if available.

You can also set it up to be site specific by adding general.useragent.override.SITEADDRESSHERE.COM

And for each site specific one you add you can either use a desktop string or a mobile string to suit your preference.

Here are a couple of strings;

Desktop View/Mode: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:41.0) Gecko/20100101 Firefox/45.0.1

Mobile View/Mode: Mozilla/5.0 (Android 4.4.2; rv:42.0) Gecko/42.0 Firefox/45.0.1

Oh, also make sure you enable general.useragent.site_specific_overrides by setting it to TRUE.

I hope this helps.

Hi There, Thanks for your tips. I did your first suggestion and set general.useragent.site_specific_overrides to True, but it didn't work. Moreover vogue.it actually has a mobile version, in fact, my friend can correctly display it on his phone and I did the same when I used Chrome on my mobile device.

Is it possible your friend was using the vogue.it app instead of a browser page? I was unable to find any difference between viewing the vogue.it page in mobile mode or in desktop mode, but I was able to find they have an app in the apple store, which displays all its sites pages inside the mobile app: https://itunes.apple.com/us/app/vogue-italia/id592704749?mt=8

But then again, you said it worked for you in Chrome. Could you post screen shots of both versions so I can see the differences?

Normally I wouldn't go this much in depth, but now it's bothering me too! Hehe.

Below is a screen shot of how the pages look in the app:

I think I figured it out!

I loaded the site with my smartphone instead of my tablet & I see now that it displays a less robust site when I use a smaller screen device.

I'm assuming the site somehow knows the users screensize and displays the page accordingly. This still doesn't explain how you were able to see the mobile version on chrome but not in Firefox, maybe someone else can weigh in on this?