Firefox 57 and later do not support any API to make this extension work. If you prefer your browser tabs without close buttons, you can make it work by adding a custom userChrome.css file to your Firefox profile:

1. Find your profile folder

1. Create a directory called chrome inside it if one does not already exist

1. Create a file named userChrome.css in the new directory

1. Add the following CSS code to it:

   @namespace url("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul");
   .tab-close-button { display: none !important; }

1. Restart Firefox

Source : https://github.com/djc/no-close-buttons More information : http://kb.mozillazine.org/index.php?title=UserChrome.css

I have mac and cannot find my profile folder .. Thank you.

I am sorry .. I need more detail or help than this ..

http://kb.mozillazine.org/index.php?title=UserChrome.css

On Mac : ~/Library/Mozilla/chrome/userChrome.css ~/Library/Application Support/chrome/userChrome.css

I appreciate your response .. However .. I do not have the folders :(

Please read article before ...

"Go to your profile folder. Then go to the chrome folder there, creating it if necessary. In the chrome folder, create a plain text file named userChrome.css" http://kb.mozillazine.org/index.php?title=UserChrome.css

I do not have chrome .. I have Firefox .. I found .. Applications Support/Firefox/Pofiles ..

Please confirm what you mean by directory .. Thank you.

You can use the button on the "Help -> Troubleshooting Information" (about:support) page to go to the current Firefox profile folder or use the about:profiles page.

• Help -> Troubleshooting Information -> Profile Directory:
  Windows: Show Folder; Linux: Open Directory; Mac: Show in Finder
• http://kb.mozillazine.org/Profile_folder_-_Firefox
• ~/Library/Application Support/Firefox/Profiles/<profile>/

In Mac OS X v10.7 and later, the ~/Library folder in the Home directory is a hidden folder.

• http://kb.mozillazine.org/Show_hidden_files_and_folders#Mac_OS_X

• create the chrome folder (lowercase) in the <xxxxxxxx>.default profile folder if this folder doesn't exist
• use a plain text editor (Mac: Textedit; Windows: Notepad) to create a (new) userChrome.css file in the chrome folder (file name is case sensitive)
• paste the code in the userChrome.css file in the editor window
• make sure that the userChrome.css file starts with the default @namespace line

cor-el said

You can use the button on the "Help -> Troubleshooting Information" (about:support) page to go to the current Firefox profile folder or use the about:profiles page.

• Help -> Troubleshooting Information -> Profile Directory:
  Windows: Show Folder; Linux: Open Directory; Mac: Show in Finder
• http://kb.mozillazine.org/Profile_folder_-_Firefox
• ~/Library/Application Support/Firefox/Profiles/<profile>/

In Mac OS X v10.7 and later, the ~/Library folder in the Home directory is a hidden folder.

• http://kb.mozillazine.org/Show_hidden_files_and_folders#Mac_OS_X

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• create the chrome folder (lowercase) in the <xxxxxxxx>.default profile folder if this folder doesn't exist
• use a plain text editor (Mac: Textedit; Windows: Notepad) to create a (new) userChrome.css file in the chrome folder (file name is case sensitive)
• paste the code in the userChrome.css file in the editor window
• make sure that the userChrome.css file starts with the default @namespace line

I was able to do this .. But it is not working .. The userChrome.css file has a Safari symbol .. I got info and changed the open with Safari to Firefox ..

userChrome.css get info says: Kind: Text Document Where: /Users/Adele/Library/Application Support/Firefox/Profiles/********.default/chrome (I made the stars) Name and Extension: userChrome.css Open with: Firefox

I still have the X close tab button showing on all tabs :(