I have FF 18.104.22.168 and Windows XP Pro, and had FF set as default browser for months (years?). I also use Dreamweaver. The two have existed together peacefully.
A day or so ago I clicked a "yes" to something that looked logical .. and promptly forgot what it was.
The problem, now when I try to open a local file with FF it defaults to Dreamweaver and opens Dreamweaver which opens the file. When I'm using Dreamweaver and do the F12 browser check, it basically blinks and defaults back to the Dreamweaver page.
I looked at Windows Explorer > Folder Options > File Types and both Dreamweaver and FF are "Recommended Programs".
When I look at FF Content > Manage File Types, I see options for handling files. If I remove PHP and then try to open a PHP file, I get the windows prompt asking what application to use. I think I did this before and selected the "Always do this" .. and FF starts opening tabs like crazy .. but all pages are blank.
That's not it. If I set FF as my default browser, I still get the "What do You Want to Do With this File" prompt and if I click "Open", I get a new tab with blank page .. and again, and again .. ad infinitum.
FF opens .htm files just fine, but goes nuts on .php.
I mistakenly checked the "always do this" box and FF starts looping?, opening new tabs, one after another. Even when I try to close FF, it does close, but then relaunches and starts opening new tabs again.