security padlock icon doesn't come on when I purchase items on line since I upgraded to Firebfox 4

I upgraded to Firefox 4 yesterday. Since doing the upgrade the yellow security padlock icon doesn't come on when I am typing my credit card number when making a purchase on the internet. Before finishing the upgrade a window opened stating something about the Kaspersky url wasn't compatible with Firefox 4. When I click on the Kaspersky icon the screen that opens states that my computer is protected from viruses. I'm concerned that my credit card number might not be secure when making purchases on the internet following this upgrade. The security padlock icon always came on with the previous version of Firefox. Thank you, Tom Hanaway