Hallo nOlivier,

Would you please take a look at this :

https://developer.mozilla.org/de/docs/Tools/bildschirmgroessen-testen

Is that helpful in any way  ?

see the screenshot. if i click to webmaster tools >Screen size testing, i get the message:

"Das Testen von Bidschirmgrößen steht nur in externen Browser-Tabs zur Verfügung"

"Screen size testing is only available in external browser tabs"

best regards

n.Olivier

nOlivier said

"Das Testen von Bidschirmgrößen steht nur in externen Browser-Tabs zur Verfügung"

I had seen it .....

Unfortunately the only thing I could find was the article I gave you a link to (sorry .... )

But I'm sure that someone else will come up with the perfect solution for you.

Looks that you disabled multi-process tabs.

You can check this pref on the about:config page and make sure it is default (true).

• browser.tabs.remote.autostart = true

You can open the about:config page via the location/address bar. You can accept the warning and click "I accept the risk!" to continue.

• http://kb.mozillazine.org/about:config

See also:

• https://support.mozilla.org/en-US/kb/performance-settings

thanks - solved

greetings Olivier

nOlivier said

thanks - solved

That's great  !

Would you be so kind as to mark cor-el's post as
Chosen Solution  ? ('Solved the problem' button to the right)

Thank you in advance  !

Sorry, I did not see it.