In Firefox 40 and 41 you can probably remove this notification by setting full-screen-api.approval-required to false.

You can open the about:config page via the location/address bar. You can accept the warning and click "I'll be careful" to continue.

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

This method doesn't work in Firefox 42.The setting "full-screen-api.approval-required" already set as false.

How I disable that message on new versions of Firefox??

Thank you!

That pref is no longer supported in Firefox 42 and later, so you can't use this to hide the message.

• [/questions/1092553] Removing the "Press Esc To Exit Full Screen Mode"

Add code to the userChrome.css file below the default @namespace line.

• http://kb.mozillazine.org/userChrome.css

@namespace url("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"); /* only needed once */

#full-screen-warning-container{display:none!important}

The customization files userChrome.css (user interface) and userContent.css (websites) are located in the chrome folder in the Firefox profile folder.

• http://kb.mozillazine.org/Editing_configuration

You can use this button to go to the current Firefox profile folder:

• Help > Troubleshooting Information > Profile Directory: Show Folder (Linux: Open Directory; Mac: Show in Finder)
• http://kb.mozillazine.org/Profile_folder_-_Firefox

You can modify these prefs on the about:config page to disable the fade in and fade out. Leave out the quotes around the value (enter only two zeros separated by a space).

• full-screen-api.transition-duration.enter: "0 0"
• full-screen-api.transition-duration.leave: "0 0"

the files userChrome.css and userContent.css don't exist in the given directory. When I create them and fill them with the text above, I see no effect on the full screen message, so unfortunately this doesn't solve the problem.

Did you verify that Windows hasn't appended a hidden .txt file extension?

Also make sure that userChrome.css is a plain text file.

Can you post the content of the userChrome.css file and possibly a screenshot that shows the location (directory listing) in details format?

The directorylisting is: C:\Users\Arnold\AppData\Roaming\Mozilla\Firefox\Profiles\e0va8jm7.default-1417165857948\extensions\idme@abine.com\chrome. I added a screenshot of it. The file userChrome.css is a plain text file (made with Notepad++). It doesn't have a hidden .txt extension and it contains: @namespace url("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"); /* only needed once */

1. full-screen-warning-container{display:none!important}

That's it! Greetings, Arnold

That is the wrong location as that is in the folder of an extension. You need to create the chrome folder in the main e0va8jm7.default-1417165857948 folder.

• C:\Users\Arnold\AppData\Roaming\Mozilla\Firefox\Profiles\e0va8jm7.default-1417165857948\chrome\userChrome.css

Yes, that works well! The chrome subdirectory didn't exist yet in the main folder so I had to create it first, and that's what caused the confusion. Thank you!

You're welcome.

An easier work-around might be changing full-screen-api.warning.delay and full-screen-api.warning.timeout to 0 in about:config. I tested this on FF 43.0.3 and it worked for me

Hi edvardgrieg11, full-screen-api.warning.timeout is a new setting in Firefox 43, so setting that to 0 (show for 0 milliseconds) is now the easiest way to prevent the message from appearing.