It must be because of Kaspersky has not yet added support for the new update. Just wait, and a update from Kaspersky should be coming.

If you believe this to be a FireFox problem try resetting Firefox

Hello,

The Reset Firefox feature can fix many issues by restoring Firefox to its factory default state while saving your essential information. Note: This will cause you to lose any Extensions, Open websites, and some Preferences.

To Reset Firefox do the following:

1. Go to Firefox > Help > Troubleshooting Information.
2. Click the "Reset Firefox" button.
3. Firefox will close and reset. After Firefox is done, it will show a window with the information that is imported. Click Finish.
4. Firefox will open with all factory defaults applied.

Further information can be found in the Refresh Firefox - reset add-ons and settings article.

Did this fix your problems? Please report back to us!

Thank you.

Add-ons have to be compatible with Firefox, not the other way around.

Kaspersky usually takes at least a week after to a new Firefox release to update their product(s). I suppose they do not use the beta test period for Firefox to get their updates ready in advance unlike some other security software vendors.

Some information about how the Kaspersky add-ons are not totally "critical" and not totally "necessary" for your protection from a Kaspersky forum Moderator - http://forum.kaspersky.com/index.php?showtopic=247647&view=findpost&p=2021200