The latest blog entry from the IE team makes for interesting reading.
IEBlog : IE December Security Update – addressing scattered reports of odd browser behavior:
What can I say apart from “TOLD YA SO”.
An MVP came to me the other week, asking for information about a “workaround” that he heard could be used to allow Internet Explorer 6 to be run side by side with Internet Explorer 7. My response was that I knew of this “hack” (I refuse to call it a workaround) but I strongly discouraged him from using it. I warned him that it was unsupported and would cause problems – perhaps not problems he could see right now, but they would occur.
When I asked him why he wanted to run IE6 and IE7 together, the only reason he gave was that some sites do not work with IE7. He was surprised to discover that this is an issue that is easily addressed, without running the risk of causing problems for your PC (such as those being reported to the IE team). Advice and instruction on how to get around User Agent String sniffing, which is in 99.9% of times the only reason you may see problems trying to access a web site when running IE7, can be found here:
I agreed, developers sometimes need to test their sites and programs against multiple browser versions. Two suggestions – Virtual PC or multiple computers. As Developers with access to MSDN we can do this. As professionals we should not be using hacks to get our work done – as the IE team’s report illustrates very well, hacks are not the way to go – you cannot predict what may be happening behind the scenes.
There was, once, a ‘usability mode’ years ago that allowed us to run IE4 at the same time as IE5 or 5.5, but that that protocol is no longer in use: