The checkboxes decorated with RadFormDecorator appeared double in Classic rendering after upgrading to Firefox 63.

Steps to reproduce:
1. Upgrade to Firefox 63
2. Run the following setup
        <telerik:RadFormDecorator runat="server" DecoratedControls="CheckBoxes" RenderMode="Classic" />
        <div>asp:Checkbox</div>
        <asp:CheckBox ID="chkApproved" runat="server" Text="asp:Checkbox" />

        <div>Html Input</div>
        <input id="chkApproved1" type="checkbox" name="chkApproved" />

======================================

Solutions found so far:
1) Use RadFormDecorator in Lightweight RenderMode:
     <telerik:RadFormDecorator runat="server" RenderMode="Lightweight"/>

2) Set the RadFormDecorator's DecoratedControls="All":
     <telerik:RadFormDecorator runat="server" RenderMode="Classic" DecoratedControls="All"  />

3) Set the ControlsToSkip="CheckBoxes"
      <telerik:RadFormDecorator runat="server" RenderMode="Classic" ControlsToSkip="CheckBoxes"  />

4) Or add the following CSS overwrite to the page:
        <style>
           .rfdCheckboxUnchecked, .rfdCheckboxChecked {
               padding: 0 !important;
               background-image: none !important;
           }
       </style>

After upgrading to new version of Telerik (2016.3.914.35), duplicate checkboxes are displaying. Please refer attached file.

The appearance of disabled inputs in the markup is not updated in IE11. For the time being you can manually set the corresponding disabled CssClasses, using the approach from this help article:

http://www.telerik.com/help/aspnet-ajax/formdecorator-troubleshooting-input-appearance-is-not-updated-when-disabled-in-internet-explorer.html

In Q3 2013 Firefox and Chrome freeze when a container with a select element is made visible with JavaScript and RadFormDecorator is present on the page.

The issue will be fixed for the upcoming Q3 2013 SP1. For the time being possible workarounds are:

    - Setting the ControlsToSkip property of the RadFormDecorator to "Select".
    - OR placing the provided JavaScript code from the attached archive below the declaration of the RadFormDecorator.

Sample scenarios that reproduce the issue are:

    - Expanding an inner item from a RadPanelBar. The RadPanelBar has multiple Items that contain select elements and a RadFormDecorator is present on the page.
    - JavaScript is used to set the display property of a container with a select element to "block" for example, multiple containers with select elements are present on the page and RadFormDecorator is used. For example:
JavaScript:

<script type="text/javascript">
    function pageLoad() {
        $get("div1").style.display = "block";
    }
</script>

ASPX:

<telerik:RadFormDecorator ID="RadFormDecorator1" runat="server" DecoratedControls="All" />
<div id="div1" style="display: none;">
    <select>
        <option>text1</option>
        <option>text2</option>
        <option>text3</option>
    </select>
</div>
<div id="div2" style="display: none;">
    <select>
        <option>text1</option>
        <option>text2</option>
        <option>text3</option>
    </select>
</div>

Workarounds:
- use RenderMode="Lightweight"
- OR, set DecoratedControls="All"

Repro:

			<telerik:RadFormDecorator ID="RadFormDecorator1" runat="server" DecoratedControls="Textbox,Textarea,Buttons,Scrollbars,Select,CheckBoxes,RadioButtons"
				 Skin="Default" RenderMode="Classic" />
			<div class="container body-content">
				<h2>First Application </h2>
				<p>SFSFSDF</p>

				<br />
				<asp:RadioButtonList runat="server" ID="dlSchdId" RepeatColumns="6" RepeatDirection="Horizontal"
					Width="100%">
					<asp:ListItem Text="test 1"></asp:ListItem>
					<asp:ListItem Text="test 2"></asp:ListItem>
				</asp:RadioButtonList>

				<asp:CheckBox runat="server" ID="chk1" Text="Check Box 1" />
			</div>

For the time being the following CSS workaround can be used:

    <style>
        .rfdSelect.rfdSelect_Default {
            min-height: 1.417em;
        }
    </style>

For the time being you can either skip the selects elements from decoration:

ASPX:

        <telerik:RadFormDecorator ID="RadFormDecorator1" runat="server" DecoratedControls="All" ControlsToSkip="Select" />
        <div id="div1">
            <telerik:ReportViewer ID="ReportViewer1" runat="server" Height="492px" Width="927px"></telerik:ReportViewer>
        </div>


Or decorate only particular zone that do not include the ReportViewer:

ASPX:
        <telerik:RadFormDecorator ID="RadFormDecorator1" runat="server" DecoratedControls="All" DecorationZoneID="div2" />
        <div id="div1">
            <telerik:ReportViewer ID="ReportViewer1" runat="server" Height="492px" Width="927px"></telerik:ReportViewer>
        </div>
        <div id="div2">
            <input type="text" name="name" value=" " />
            <select>
                <option>option1</option>
                <option>option2</option>
                <option>option3</option>
            </select>
        </div>

Buttons decorated by RadFormDecorator have 16 additional pixels. Issue is reproducible since Q3 2013 and is caused due to the box-sizing and -moz-box-sizing styles. For the time being one of the following workarounds can be used:

1) Override the box-sizing style:

CSS:

    <style>
        .RadForm, .RadForm.rfdTextbox .rfdDecorated {
            box-sizing: border-box !important;
            -moz-box-sizing: border-box !important;
        }
    </style>

ASPX:

        <telerik:RadFormDecorator ID="RadFormDecorator1" runat="server" DecoratedControls="All" />
        <div style="margin: 20px; margin-bottom: 0; border: 2px solid Black; height: 15px; width: 168px;"></div>
        <div style="position: absolute; margin: 10px; margin-top: 0; padding: 10px; padding-top: 0;">
            <div>
                <asp:Button ID="Button1" runat="server" Text="Cancel" TabIndex="1" Width="80px" UseSubmitBehavior="false" />
                <asp:Button ID="Button2" runat="server" Text="Save" TabIndex="2" Width="80px" UseSubmitBehavior="false" />
            </div>
        </div>
2) Set the rendermode of the FormDecorator to lightweight:

ASPX:

        <telerik:RadFormDecorator ID="RadFormDecorator1" runat="server" DecoratedControls="All" RenderMode="Lightweight" />
        <div style="margin: 20px; margin-bottom: 0; border: 2px solid Black; height: 15px; width: 168px;"></div>
        <div style="position: absolute; margin: 10px; margin-top: 0; padding: 10px; padding-top: 0;">
            <div>
                <asp:Button ID="Button1" runat="server" Text="Cancel" TabIndex="1" Width="80px" UseSubmitBehavior="false" />
                <asp:Button ID="Button2" runat="server" Text="Save" TabIndex="2" Width="80px" UseSubmitBehavior="false" />
            </div>
        </div>

For the time being the following CSS can be used:

    <style>
        .rfdSelectBox.rfdSelectBox_Default.rfdSelectBoxDropDown {
            z-index: 4007;
        }
    </style>

Where 'Default' is the name of the skin.

Issue is reproducible with the following markup:

ASPX:

<telerik:RadFormDecorator ID="RadFormDecorator1" runat="server" DecoratedControls="All" RenderMode="Lightweight" />

        <select>
            <option>option 1</option>
            <option selected="selected"></option>
        </select>


For the time being the following JavaScript workaround can be placed below the RadFormDecorators' declaration:

        <telerik:RadFormDecorator ID="RadFormDecorator1" runat="server" DecoratedControls="All" RenderMode="Lightweight" />
        <script>
            Telerik.Web.UI.FormDecorator.LightWeightDomDecorator.prototype.setSelectHeaderText = function (decoratedSelectHeader, text, isDropDown) {
                if (isDropDown) {
                    decoratedSelectHeader.innerHTML = "";
                    var span = this._createArrowSpan();
                    decoratedSelectHeader.appendChild(span);
                    decoratedSelectHeader.appendChild(document.createTextNode(text));
                } else {
                    var innerElement = $telerik.getElementByClassName(decoratedSelectHeader, "rfdSelectText");
                    if (text) text = text.replace(/</g, "&lt;");
                    if (innerElement) innerElement.innerHTML = text;
                }
            }
        </script>

For the time being you can use the following JavaScript workaround:
<html xmlns="http://www.w3.org/1999/xhtml">
<head id="Head1" runat="server">
	<title></title>
	<script src="//ajax.googleapis.com/ajax/libs/jquery/1.8.3/jquery.min.js"></script>
	<script src="//ajax.googleapis.com/ajax/libs/jqueryui/1.10.4/jquery-ui.min.js"></script>
</head>
<body>
	<form id="form1" runat="server">
		<telerik:RadScriptManager ID="RadScriptManager1" runat="server">
		</telerik:RadScriptManager>
		<telerik:RadFormDecorator ID="RadFormDecorator1" runat="server" />
		<script>
			//Workaround:
			var removeCssClass = Sys.UI.DomElement.removeCssClass;
			Telerik.Web.UI.RadFormDecorator.prototype.set_elementDisabled = function (element, val) {
				var actor = element;
				var nextSibling = element.nextSibling;
				var type = element.type;

				if ((type == "checkbox" || type == "radio") && nextSibling && nextSibling.tagName == "LABEL") {
					actor = nextSibling;
				}
				else if (type == "button" || type == "reset" || type == "submit" || element.tagName == "BUTTON") {
					var parent = element.parentNode;
					if (parent && parent.tagName == "A") {
						actor = parent;
						parent.disabled = val;
					}
				}
				if (val) addCssClass(actor, "rfdInputDisabled");
				else removeCssClass(actor, "rfdInputDisabled");
				try {
					if (!val && $telerik.isIE && actor.parentNode.disabled) {
						actor.parentNode.disabled = val;
					}
				} catch (e) {
				}
			}
		</script>
		<input type="button" value="Test" onclick="Run(); return false;" />
		<div id="TestDiv" style="display: none"></div>
		<script type="text/javascript">
			function Run() {
				$('#TestDiv').dialog({
					modal: true,
					buttons: { "OK": function () { alert('bye'); } }
				});
			}
		</script>
	</form>
</body>
</html>

The issue is reproducible when you add a CSS class, responsible for styling the scrollbars, too lately and can also be reproduced on a page that contains no Telerik UI for ASP.NET AJAX controls:

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title></title>
    <style>
        .RadForm.rfdScrollBars.RadForm_WebBlue div::-webkit-scrollbar,
        .RadForm.rfdScrollBars.RadForm_WebBlue div::-webkit-scrollbar-thumb:vertical,
        .RadForm.rfdScrollBars.RadForm_WebBlue div::-webkit-scrollbar-thumb:horizontal {
            background-color: red !important; /* choose your color */
        }
    </style>
</head>
<body>
    <form id="form1" runat="server">
        <telerik:RadScriptManager ID="RadScriptManager1" runat="server"></telerik:RadScriptManager>
        <script>
            setTimeout(function () {
                Sys.UI.DomElement.addCssClass(document.documentElement, "RadForm RadForm_WebBlue rfdScrollBars");
            }, 10);
        </script>
        <div id="testDiv" style="overflow: scroll; height: 200px; width: 300px">
            <table>
                <tr style="height: 500px;">
                    <td></td>
                </tr>
            </table>
        </div>
    </form>
</body>
</html>

If you remove the timeout, however, the issue will be gone:

        <script>
        //    setTimeout(function () {
                Sys.UI.DomElement.addCssClass(document.documentElement, "RadForm RadForm_WebBlue rfdScrollBars");
         //   }, 10);
        </script>

Possible workarounds for scenarios when the RadFormDecorator control is involved:

    1) Remove the scorllbars styling by setting the ControlsToSkip property to "Scrollbars".

<telerik:RadFormDecorator ID="RadFormDecorator1" runat="server" DecoratedControls="All" ControlsToSkip="Scrollbars" />

     2) Use the following JavaScript workaround:
	<form id="form1" runat="server">
		<telerik:RadScriptManager ID="RadScriptManager1" runat="server"></telerik:RadScriptManager>
		<telerik:RadSkinManager ID="RadSkinManager1" runat="server" Skin="Glow"></telerik:RadSkinManager>
		<telerik:RadFormDecorator ID="RadFormDecorator1" runat="server" DecoratedControls="All" ControlsToSkip="Scrollbars" />
		<script>
			//JavaScript workaround:
			Telerik.Web.UI.RadFormDecorator.removeGlobalClassesToRootElement = function (rootElement) {
				rootElement.className = rootElement.className.replace(/rfdRtl|RadForm_\w+|rfdButton|rfdZone|rfdLabel|rfdHeading|rfdTextbox|rfdTextarea|rfdFieldset|rfdRadio|rfdCheckbox|rfdGrids/g, "").trim();
			};
			Sys.UI.DomElement.addCssClass(document.documentElement, "RadForm RadForm_<%=RadSkinManager.GetCurrent(this.Page).Skin%> rfdScrollBars");
		</script>
		<div id="testDiv" style="overflow: scroll; height: 200px; width: 300px">
			<table>
				<tr style="height: 500px;">
					<td></td>
				</tr>
			</table>
		</div>
	</form>

Workaround - Set the EnableScriptCombine property of RadScriptManager to false or remove RadFormDecorator.