DD Thank you! Found something else. The reason why code didn't work sometimes was focus of UniHTMLMemo!!!   When i clicked to UniHTMLMemo before clicking ImageUpload so that caret appear everything works in Chrome, Opera, FireFox!!!   So i tried to change code like this   procedure TMainForm.UniHTMLMemo1AjaxEvent(Sender: TComponent; EventName: string; Params: TStrings); begin if EventName = 'uploadImage' then begin UniHtmlMemo1.SetFocus; // doesn't work with that UniFileUp