We have for some time stated on our proposals that we do not support Internet Explorer 6. This is a stance that Google (and others) have taken. IE6 is 11 years old and is, in our opinion, very buggy and time-consuming to support. We find that IE6 fixes can break HTML5 validation so we have drawn the line under that release. For IE we generally test on IE8 and 9 (as it stands today). We will support IE6 if we have a customer requirement but we make it clear that additional development time will be needed.
Firefox is generally fairly web standards compliant, we test against the latest version and are prepared to investigate any problems back to around v 3.5.
We will test our sites against latest versions of Safari and Chrome, we do not generally test Opera or any other browsers.
We write our code to HTML5 standards taking care that any “new” HTML5 features have fallbacks where possible (e.g differing video formats supported by different browsers).
If you have any questions about browser support or any special website development requirements then do get in touch.