Firefox shouldn't have any issues with security applications as it is a fairly standards compliant browser. It may not be entirely Firefox's fault, it could be using another module and that is at fault. That is why I suggested clicking the more information, etc. to see more information about the reason.
I'm still using 2.0.0.2, will be updating later today, but it may be better to download the complete latest version of firefox and save it so you can find it later, uninstall the current installation and reboot, then install the latest version. Something else you could try is to run firefox from the Safe Mode link in, Start, All Programs, Mozilla Firefox. This starts firefox without extensions, if you have no problems then it might just be a troublesome extension and that may be pointed out in the 'more information' I spoke about.
I'm probably more baffled than you as to why this can't protect email is displayed on boot, I have exhausted the major reasons this may occur.
I believe you said you have tried the avast reinstall before, what I would suggest is you download the avast! Uninstall Utility,
find it here and save it to your HDD so you can find it later. Now uninstall using add remove programs, reboot, run the uninstall utility, reboot and install.