Firefox misrecognising php files
I've discovered a problem that's almost certainly due to Firefox, and wonder if anyone else has seen it, and solved it.
On one of my Firefox installations, browsing to some tiki pages results in an attempt to download a file. In my other FF installations, things work fine.
For example, on FF installation A, when I browse to .../tiki-listpages.php, FF attempts to download a file of that name. But on FF installation B, the page opens as expected.
So FF installation A misrecognises some php files, and I suppose I've got a setting or an extension that's responsible.
Before I go disabling extensions etc, I would like to hear if this is a known problem and has a ready solution. Have you seen it?