> I should have been clearer; the program saves all
> the pages in html format, but it saves many of them
> with a php extension. I thought that was why Firefox

The latest beta keeps the extentions the same the site (php, html, .shtml.)
3.32 always renamed them to .html

I have also seen firefox repeatedly reload a page in the 3.4x (non-beta)
versions. In the same tab in my case.  The file was an obvious not a valid
mirrored file.  An update fixed the file(s).