The Acid2 test Microsoft’s still top-secret Internet Explorer 8 passed what is known as the Acid2 test. Acid2 is a test case designed by the Web Standards Project to discover, if possible, errors with rendering Web pages in browsers and Web authoring tools. Basically, it tests how a browser or tool works with features from various Web standards.
There are many Web Browsers available on the market. Almost all of them are free and yet they have their own "Complications" in rendering a same site in different way. Any web developer's headache is to make sure that their website looks same on different kind of browsers.. Ah.. Given the wealth of browsers and versions along with operating systems, this is easier said than done.
Does that means if you test your web application with this 4 browsers will solve the issue?
Don't forget the amount of Windows Mobile and other PDA is coming up daily, Each of the PDA and smart phones, they have their unique browser rendering system along with different screen sizes..
Anyway, how you should test your site with multiple browsers? You will found out that the most problems comes from Internet Explorer rendering of sites. Internet Explorer tends not to follow the W3C web standards for browser rendering. Yes I know you can put few on your system but there is a huge rendering gap between Internet Explorer 6 and 7. So how you want to test using IE6 and IE7 in the same machine. Well you can't Install all of them together cause they are using same DLL names and libraries. Technology has the advantage to give solutions in this situations.
Are you looking for older browsers or a place where you can find all kind of browsers archive then don't forget to check out Older Browsers Archive at evolt.org. Another path that may be followed is using a third-party service to test a Web application via multiple browser platforms. You could choose an offshore company to test with various platforms or use a free service like Browsershots or a paid service like BrowserCam.
The boom in mobile device usage means this ever-expanding user community should not be ignored. Like personal computers, you can assemble a group of mobile devices to use for testing, or you can use third-party services and products to assist with mobile testing. A great resource is the DotMobi Virtual Developer Lab, which provides access to hundreds of mobile devices for testing.
While most developers think an application is ready once their work is done, you still need to conduct extensive testing to ensure the product delivered actually meets project expectations and behaves consistently within the target set of browsers. There are many ways to go when testing with multiple browsers as you may choose to set up multiple machines, use virtualization, or even go with a third-party service or organization