Your crashreport is:
https://crash-stats.mozilla.com/report/index/bp-513cd0e4-ffd2-4b06-9d38-8294a2111030
Firefox 7.0.1 Crash Report [@ RapportTanzan7.dylib@0x7f7f ]
This is a crash in Trusteer Rapport, based on similiar crashes on Windows machines. Updating this program should solve the problem. (At least this is confirmed on Windows with Firefox 7.0.1)
Which version / build ID of Rapport do you have exactly?
Which version of Firefox do you use? The crash is for Firefox 7.0.1, this forum is showing 3.6.11?

Sorry, I was looking at version 3.6.11 from my iMac.

I deleted the old version of Firefox on my MacBook Pro so was installing 7.0.1. I have downloaded the latest version of Trusteer Rapport and still crashing...however when I stop Rapport then Firefox works

Rapport version is 3.6.1108.38

Crash ID: bp-c1cc1b83-8a6e-42b3-8e08-4e1df2111030