Rated 5 out of 5 stars

Great! Especially for those like me who are migrating from Opera 12 (it has this feature built-in).Customization request: can remove dashed underline from the private tab title.

This review is for a previous version of the add-on (0.1.3). 

Here is some styles for userChrome.css/Stylish:
https://github.com/Infocatcher/Private_Tab#styles


To only remove underline:
https://github.com/Infocatcher/UserStyles/blob/master/Private_Tab_background/privateTabBackground-gradient.css#L88

@namespace url("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul");
@-moz-document url("chrome://browser/content/browser.xul"),
    url("chrome://navigator/content/navigator.xul") {
    /* Remove dashed underline from private tabs, https://addons.mozilla.org/addon/private-tab/ */
    .tabbrowser-tab[privateTab-isPrivate] {
        text-decoration: none !important;
    }
    .tabbrowser-tab[privateTab-isPrivate][pinned] .tab-icon-image,
    .tabbrowser-tab[privateTab-isPrivate][pinned] .tab-throbber {
        border-bottom: none !important;
    }
}