You may need to update Kaspersky to a newer version to get a compatible version of their extension. You also could check whether they've replaced it with a different one already.

You can look on the Add-ons page. Either:

• Ctrl+Shift+a (Mac: Command+Shift+a)
• "3-bar" menu button (or Tools menu) > Add-ons
• type or paste about:addons in the address bar and press Enter/Return

In the left column of the Add-ons page, click Extensions. Then:

Scan down the list on the right side; disabled extensions (grayed background) usually appear at the bottom. Do you see any new Kaspersky extensions here that are enabled or could be enabled?

Note that this is only about extensions that Kaspersky add to Firefox. Your Kaspersky security software should still work like it used to and protect you. You would normally need these extensions and they can cause a lot of issues if they aren't working properly.

When I click on extensions I get a box saying - you don't have any add-ons of this type installed. And a box saying - Missing some thing? Some extensions are no longer supported by Firefox. Show legacy extensions.

Clicking on legacy extensions takes me back to original warning. I'm really fed up - legacy extensions? My grandmother's braids?