This is "as designed" See bug https://bugzilla.mozilla.org/show_bug.cgi?id=854126

You can use an extension to get Private Browsing mode support per tab.

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

Private Browsing mode tabs get a dashed underline You can toggle Private Browsing mode on/off via the right-click context menu of a tab You will also see a purple mask on the Tab bar.

You might need to use a custom style rule to modify the appearance of the toolbar area or, if you prefer, just the tabs bar, or maybe just the very top of it.

For example:

To turn the tabs bar background dark purple on a private window in a regular session:

#main-window[privatebrowsingmode="temporary"] #TabsToolbar {
  background-color: #303 !important;
}

or the whole toolbar area:

#main-window[privatebrowsingmode="temporary"] #navigator-toolbox {
  background-color: #303 !important;
}

Screenshot comparison attached. The best colors will vary depending on your lightweight theme.

Custom style rules can be applied to Firefox's interface area using either the Stylish extension or a userChrome.css file. Someone can provide details if you don't find a more convenient solution.

jscher2000 said

You might need to use a custom style rule to modify the appearance of the toolbar area or, if you prefer, just the tabs bar, or maybe just the very top of it. For example: To turn the tabs bar background dark purple on a private window in a regular session:

#main-window[privatebrowsingmode="temporary"] #TabsToolbar {
  background-color: #303 !important;
}

or the whole toolbar area:

#main-window[privatebrowsingmode="temporary"] #navigator-toolbox {
  background-color: #303 !important;
}

Screenshot comparison attached. The best colors will vary depending on your lightweight theme.

Custom style rules can be applied to Firefox's interface area using either the Stylish extension or a userChrome.css file. Someone can provide details if you don't find a more convenient solution.

This works great. I couldn't get the second option to work, but the first worked passably enough.