A bookmarklet to let you write notes stored in your localstorage for the domain you're currently on.

Domain_Notes_Bookmarklet.js

javascript:(function(){
	var parentID = 'a3q_parent';
	var dID = 'a3q_customNotes';
	var buttonID = 'a3q_close_button';
	var saveThrottleSpeed = 100;
	var lastSave = Date.now();
	var waitCallback;

	function a3q_Save(force){
		force = force || false;
		clearTimeout( waitCallback );
		if( force || Date.now() - lastSave >= saveThrottleSpeed ) {
			lastSave = Date.now();
			localStorage.setItem( 'a3q_note', a3q_GetContents() );
		} else {
			waitCallback = setTimeout(function(){
				a3q_Save();
			}, saveThrottleSpeed - Date.now());
		}
	};

	function a3q_Load() {
		return localStorage.getItem( 'a3q_note' ) || '';
	};

	function a3q_GetContents() {
		return document.getElementById( dID ).innerHTML;
	};

	function a3q_Unload() {
		a3q_Save( true );
		d.removeEventListener( 'onkeyup', a3q_Save );
		d.parentNode.removeChild( d );
		c.removeEventListener( 'onclick', c.onclick );
		c.parentNode.removeChild( c );
	};

	var d = document.getElementById( dID );
	var c = document.getElementById( buttonID );
	if ( d ) {
		a3q_Unload();
	} else {
		var d = document.createElement( 'div' );
		d.id = dID;
		d.innerHTML = a3q_Load();
		d.style.backgroundColor = '#333';
		d.style.color = '#ccc';
		d.style.border = '1px solid #ccc';
		d.style.position = 'fixed';
		d.style.width = '800px';
		d.style.height = '600px';
		d.style.left = 'calc(50% - 400px)';
		d.style.top = 'calc(50% - 300px)';
		d.style.padding = '5px';
		d.style.zIndex = 10000;
		d.contentEditable = true;
		document.body.appendChild( d );
		d.focus();
		var lastRun = Date.now();

		d.onkeyup = a3q_Save;
		var c = document.createElement( 'button' );
		c.style.position = 'fixed';
		c.id = buttonID;
		c.style.zIndex = 10000;
		c.style.top = 'calc(50% + 300px)';
		c.style.left = 'calc(50% + 350px)';
		c.innerHTML = 'Close';
		c.style.backgroundColor = '#333';
		c.style.color = '#ccc';
		c.onclick = function(){
			a3q_Unload();
		};
		document.body.appendChild( c );
	}
})();