Export Synced Tabs List to "bookmarks.html" file (Browser Console script)

syncedTabsToBookmarksHTML.js

// Run code in Browser Console after enabling chrome debugging --
// about:config => devtools.chrome.enabled => true
// https://developer.mozilla.org/docs/Tools/Browser_Console
try {
	var tabPromise = SyncedTabs._internal.getTabClients();
	tabPromise.then((arrDevices) => {
		if (arrDevices && arrDevices.length > 0){
			// Generate a string with the format of a bookmark export file
			var d, e, out = '<!DOCTYPE NETSCAPE-Bookmark-file-1>\n<META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=UTF-8">\n<TITLE>Bookmarks</TITLE>\n<H1>Bookmarks Menu</H1>\n<DL><p>\n';
			const escapeHtmlEntities = function(aText){return (aText || '').replace(/&/g, '&amp;').replace(/</g, '&lt;').replace(/>/g, '&gt;').replace(/"/g, '&quot;').replace(/'/g, '&#39;')};
			for (var j=0; j<arrDevices.length; j++){
				// Create a folder for each device
				d = new Date(arrDevices[j].lastModified);
				e = Math.floor(d.getTime()/1000);
				out += '<DT><H3 ADD_DATE="' + e + '" LAST_MODIFIED="' + e + '">Synced Tabs from ' + escapeHtmlEntities(arrDevices[j].name) + ' as of ' + d.toString() + '</H3>\n<DL><p>\n';
				// Sort tabs by most recently used
				var arrTabs = arrDevices[j].tabs;
				arrTabs.sort(function(a, b){return b.lastUsed - a.lastUsed;});
				for (var i=0; i<arrTabs.length; i++){
					// Create a bookmark (link) for each tab
					d = new Date(arrTabs[i].lastUsed * 1000);
					e = Math.floor(d.getTime()/1000);
					out += '  <DT><A HREF="' + arrTabs[i].url + '" ADD_DATE="' + e + '" LAST_MODIFIED="' + e + '">' + escapeHtmlEntities(arrTabs[i].title) + '</A>\n';
					// Show last access date/time in a note (comment out or delete the next line if you don't want that)
					out += '    <DD>Last acccessed: ' + d.toString() + '\n'
				}
				out += '</DL><p>\n';
			}
			out += '</DL><p>\n</DL>';
			// Set up Save As dialog with proposed file name
			var fp = Components.classes["@mozilla.org/filepicker;1"].createInstance(Components.interfaces.nsIFilePicker);
			try { // Fx125+
				fp.init(window.browsingContext, 'Open File', Components.interfaces.nsIFilePicker.modeSave);
			} catch(e) { // Fx124 and earlier
				fp.init(window, 'Open File', Components.interfaces.nsIFilePicker.modeSave);
			}
			fp.appendFilter('HTML Files', '*.html');
			d = new Date();
			d.setMinutes(d.getMinutes() - d.getTimezoneOffset());
			var dt = d.toISOString().split('.')[0].replace(/-/g, '').replace(/:/g, '').replace(/T/, '_');
			fp.defaultString = 'bookmarks-from-synced-tabs_' + dt + '.html';
			// Call Save As dialog and (unless user cancels) write the file
			fp.open((aResult) => {
				if (aResult == Components.interfaces.nsIFilePicker.returnOK ||
					aResult == Components.interfaces.nsIFilePicker.returnReplace) {
					try {
						IOUtils.writeUTF8(fp.file.path, out);
						alert('Look for ' + fp.file.path);
					} catch (err) {
						alert(err);
					}
				} else {
					alert('Okay, not saving');
				}
			});
		} else {
			console.log('NO SYNCED TABS RETRIEVED');
		}
	}).catch((err) => {
		console.log('Problem reading or outputting synced tabs: '+err);
	});
} catch (err) {
    console.log('Problem reading or outputting synced tabs: '+err);
}

No possible way this could be made to work for private tabs open on firefox iOS as they aren't ever elligble for "sync" in the first place, correct?

That's right. You would be stuck bookmarking the private tabs and relying on bookmark sync.