Took the x out of the suffix, and it opened in IE. Stick the x back in, and it opens in Firefox when I instruct to open in IE.
Why are you still talking about the .xhtml extension? Forget you ever heard of it and just use .html (or .htm) . You don't need to know anything about it at this stage. Look through all the threads in the forums and you won't see a single one using .xhtml. You seem to have got caught up in something quite complicated that won't be relevant to you unless you are in to hard core programming and other very advanced techniques.
Concentrate on the CSS and CSS layout techniques for now.
Like we said the extension with regards to when on the server doesn't really matter: http://www.xhtmlcoder.com/beck/ uses *.xht extension though it could have equally been *.dog or an exotic *.Zebede extension I could get them all to render equally in your browser.
The extension DOES NOT always determine the MIME you'll notice if you view those pages (online) using IE 8.0 or earlier you can still view them. Because the content negotiation is used; so MSIE gets 'text/html' instead and even IE 5.0 would understand that.
The markup grammar is XHTML in both cases and nearly identical. The only difference when served as 'application/xhtml+xml' the XML Parser is triggered and it is treated as an application of XML.
To me it sounds like you are talking about offline or download files. Like said unless you have a specific reason you should be safe with 'text/html' as most modern mobile devices can cope. In which case leave those XHTML Strict 1.0 files with the *.htm extension if you find it easier...
As Paul said typically applying mobile friendly CSS will work fine if you want the content to be optimally viewed on most modern mobile devices.
It seems that, at least at this stage, persuing Xhtml is more trouble than it's worth.
Unless I find a miracle cure this week, I will abandon it and revert to html 4.01 with CSS3 whilst avoiding the use of any options that have compaitbility issues. Much of the advice givent in this thread is no doubt accuate and correct, but too far beyond my current capabilities.
Maybe when my site revamp to vs 3.0 is finished and it all looks a lot better than today, can I spend time on mastering the magic of Xhtml.
XHTML is basically a waste of time unless you have a specific need for it, which is very rare. But as has been said, there's no problem using XHTML as long as you serve it up as text/html rather than application/xhtml+xml. That said, I agree that you are better off using HTML4 and upgrading to HTML5 when that becomes mainstream. (HTML5 will accommodate what XHTML does anyway.)