cherry pick from 31b65dd, see phetsims/coulombs-law#90

js/accessibility/AccessibleSlider.js

@@ -174,6 +174,11 @@ define( function( require ) {
           this.increasedEmitter = new Emitter();
           this.decreasedEmitter = new Emitter();
 
+          // @private (a11y) - some browsers will receive `input` events when the user tabs away from the slider or
+          // on some key presses - if we receive a keydown event, we do not want the value to change twice, so we
+          // block input event after handling the keydown event
+          this.blockInput = false;
+
           // @private - entries like { {number}: {boolean} }, key is range key code, value is whether it is down
           this.rangeKeysDown = {};
 
@@ -345,6 +350,10 @@ define( function( require ) {
           var code = event.keyCode;
           this._shiftKey = event.shiftKey;
 
+          // if we receive a keydown event, we shouldn't handle any input events (which should only be provided
+          // directly by an assistive device)
+          this.blockInput = true;
+
           if ( this._enabledProperty.get() ) {
 
             // Prevent default so browser doesn't change input value automatically
@@ -458,7 +467,7 @@ define( function( require ) {
          * @param {DOMEvent} event
          */
         handleChange: function( event ) {
-          if ( this._enabledProperty.get() ) {
+          if ( this._enabledProperty.get() && !this.blockInput ) {
 
             // don't handle changes if the element does not have focus - the browser may be trying to 'commit' a new
             // value on blur that is evenly divisible by the step size, but we don't want that for AccessibleSlider