Making my web app run on all browsers

Hi I converted my web app(comrising of vb & c# files in an solution) from VS 2008 to VS 2015, It is running fine but I want to achieve the following things:

1. My web app to be cross compatible across all browsers...(Eg. Firefox,Safari,OperaMini,) In chrome(runs through IE Tab Extension) , Runs good on Internet Explorer... But on Other Browsers Images and Reports dont work or you can say doesnt work 100%

2. And do I have to Install Latest Version of Crystal Reports for VS 2015 or will previous versions work ?

3. Is there any Code to Add in Web.config to make in run on all browsers...