Heard you like CSS

@namespace url(http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul);

/* These first four rules brings back our beloved forward button, ugly selectors copied from the source because I don't want shit breaking */

/* Make the forward button always visible */
window:not([chromehidden~="toolbar"]) #urlbar-container:not(:hover) > #forward-button[disabled] {
    opacity: 1;
}

window:not([chromehidden~="toolbar"]) #urlbar-container > #forward-button[occluded-by-urlbar] {
    visibility: visible;
}

/* Make sure the urlbar stays away from the forward button */
window:not([chromehidden~="toolbar"]) #urlbar-container[forwarddisabled] > #urlbar-wrapper {
    margin-left: 4px;
}

/* Transition just makes the bar jerk back and forth when moving through history now, so remove it */
window:not([chromehidden~="toolbar"]) #urlbar-container:not([switchingtabs]) > #urlbar-wrapper > #urlbar {
    transition: none;
}


/*  All selectors beneath are used to hide their respective element
*/


/* Show close button only on active tab */
.tab-close-button.close-icon:not([selected]),

/* History marker in urlbar */
.urlbar-history-dropmarker,

/* Sync nag in hamburger menu footer */
#PanelUI-fxa-status,

/* Help button in the same footer */
#PanelUI-help,

/* Exit button, again, in that footer */
#PanelUI-quit,

/* Separators in the footer, since customize is now the only button*/
#PanelUI-footer-inner > toolbarseparator

{ display: none; }