We can see many of the web pages which are left alligned in Firefox. It can be easily fixed for all the browsers. Make the outer table <td> to be alligned center and keep the entire content in the other table like this.
<table width=”100%” cellpadding=”0″ cellspacing=”0″ border=”0″>
<!– Keep your content here –>
then what ever may be the browser, you can see the content is center alligned.