A workaround is to disable the embedded jQuery and use an older version (for example, 1.11.1 which is the previous version the suite used): https://docs.telerik.com/devtools/aspnet-ajax/controls/scriptmanager/disabling-the-embedded-jquery

Repro steps:

1. put a file explorer on the page
2. right click a file in it and select Rename
3. enter a new name, click OK

Expected: file is renamed

Actual: Firefox throws TypeError: access to strict mode caller function is censored

Sample markup

        <telerik:RadFileExplorer RenderMode="Lightweight" runat="server" ID="FileExplorer1" Width="520px" Height="310px">
            <Configuration ViewPaths="~/images" UploadPaths="~/images"
                DeletePaths="~/images"></Configuration>
        </telerik:RadFileExplorer>