Using mod_rewrite to change MIME types

I have the following code in my httpd.conf in an attempt to direct users away
from a certain page if their browser doesn't support XUL. However, all the
HTML files in the directory are sent as application/xhtml+xml which will break
non-Mozilla browsers, so I need to add the [T] flag to the end of the line.

I get a 400 (bad request) returned from the server when using non-XUL browsers.
Is there something obviously wrong here?

RewriteEngine On
RewriteLogLevel 2
RewriteLog logs/rewrite.log
RewriteCond %{HTTP_USER_AGENT} !Gecko [OR]
RewriteCond %{HTTP_USER_AGENT} Safari
RewriteRule ^/mike/chrome/chrome\.xul$ /mike/chrome/nongecko.html [L,T=text/html]

My log file says:

127.0.0.1 - - [24/Jun/2003:13:56:00 --0700]
[localhost/sid#23bb50][rid#46acc8/initial] (2) init rewrite engine with
requested uri /mike/chrome/chrome.xul
127.0.0.1 - - [24/Jun/2003:13:56:00 --0700]
[localhost/sid#23bb50][rid#46acc8/initial] (2) rewrite /mike/chrome/chrome.xul
-> /mike/chrome/nongecko.html
127.0.0.1 - - [24/Jun/2003:13:56:00 --0700]
[localhost/sid#23bb50][rid#46acc8/initial] (2) remember
/mike/chrome/nongecko.html to have MIME-type 'text/html'
127.0.0.1 - - [24/Jun/2003:13:56:00 --0700]
[localhost/sid#23bb50][rid#46acc8/initial] (2) local path result:
/mike/chrome/nongecko.html

Thanks for any help!