Убрал из своего стиля лишнее, пробуйте [spoiler][code]@namespace url("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul");
/*AGENT_SHEET*/
@-moz-document url("chrome://browser/content/browser.xul"),
    url("chrome://browser/content/bookmarks/bookmarksPanel.xul"),
    url("chrome://browser/content/history/history-panel.xul") {
#sidebar-box {
    position: fixed !important;
    width: 2px !important;
    height: auto !important;
    -moz-binding: url("data:text/xml;utf8,<bindings xmlns='http://www.mozilla.org/xbl' xmlns:xul='http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul' xmlns:xbl='http://www.mozilla.org/xbl'><binding id='sidebar'><implementation><field name='panelcontainer'>document.getAnonymousElementByAttribute(document.querySelector('%23content'), 'anonid', 'panelcontainer');</field><field name='statusbar'>document.querySelector('%23browser-bottombox');</field><field name='sidebar'>document.querySelector('%23sidebar');</field><field na

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