What themes and addons do you use? I never changed more than the stock color scheme.

GNOME theme for system integration, and the most important window altering changes I've made is to install Tree Style Tabs and hiding the top bar through userChrome.css:

    @namespace url("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul");
    
    /* to hide the native tabs */
    #TabsToolbar {
        visibility: collapse;
    }
    
    /* to hide the sidebar header */
    #sidebar-header {
        visibility: collapse;
    }

Agreed. The dev tools in Firefox are beautifully designed and a joy to use. Chrome is a dogs breakfast in comparison.