That is standard if you are using e10s tabs to distinguish them from normal tabs. The Private Tab extension does the same with Private Browsing mode tabs.

• https://addons.mozilla.org/firefox/addon/private-tab/

See also this olde blog:

• http://billmccloskey.wordpress.com/2013/12/05/multiprocess-firefox/

Thanks for your reply. :) I understand why the underlines are their, but was hoping the tab underline could be removed from the tab.

Is this possible?

See:

• chrome://browser/skin/browser.css

.tabbrowser-tab[remote] {
  text-decoration: underline;
}

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

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

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

.tabbrowser-tab[remote] {
  text-decoration: 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

Thanks again for looking at this issue. Unfortunately the steps above doesn't seems to have an effect, the underlines are still under the tabs title. I haven't tried hacking the main css file itself this is my css location: /home/user/.mozilla/firefox/<id>.default/chrome/userChrome.css (Linux)

Is this working for you? Note: I have a theme installed, but this should overrule the theme right?

Thanks again!

You can use the DOM Inspector to check what rules are applied to e10s tabs.

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

• Help > Troubleshooting Information > Profile Directory: Show Folder (Linux: Open Directory; Mac: Show in Finder)

• Create the chrome folder (lowercase) in the <xxxxxxxx>.default profile folder if this folder doesn't exist
• Use a plain text editor to create the 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

Thanks for all the help! Finaly solved the issue, by using this code: @namespace url(http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul);

.tabbrowser-tab[remote] { text-decoration: none !important; }

It seems when using @namespace url("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"); the CSS isn't loaded. When removing the quotes, it worked without any problems. Don't know if this is correct? Anyway it works now. :D

Thanks again for all the help and the quick responses. :)