Hi, I'm running Win7 x64 with ZoneAlarm Extreme Security 10.0.241.000 I had the same problem with Firefox 4. After turning off ForceField Toolbar, it started working fine. Then I updated to Firefox 5 and it wouldn't start, instead it was showing an error message from ZA... I searched mozilla support and followed the instructions here: http://kb.mozillazine.org/Browser_will_not_start_up on the topic"Firefox does not start after updating with ZoneAlarm ForceField enabled". The correct instructions for this ZA version should be: "'''Internet '''-> '''Web Security '''-> '''Settings''', and click '''Clear Virtual Data'''" After that I could open Firefox again! Then I realized it was still version 4... I installed the update, and everything went smooth. Checked again if Forcefield toolbar was inactive (it was) and opened a few pages, closed Firefox and opened again. After a while it wouldn't open... AGAIN the "Clear Virtual Data" did the trick... This time I clicked on '''Settings '''(next to "Clear Virtual Data") -> '''Advanced Settings''', and turned off "'''Enable Virtualization'''". Until ZA get a fix for this, either we turn it off or clear virtual data every few moves... Working fine. Best regards