Comment 7 for bug 309137

First of all, PHP code can't crash Firefox. PHP can generate content to crash Firefox, but it's the content, not PHP, that would cause the crash.
I generated an HTML file to test your problem. Firefox will not let you refresh repeatedly. The most I got was 2 refreshes at a time. I tested this on Firefox 3.0.10. Could you try with a new Firefox Profile? You do not need to delete your old profile to test.
https://wiki.ubuntu.com/MozillaTeam/Bugs?action=show&redirect=DebuggingFirefox#Try%20with%20a%20new%20profile