Hi billred1, I don't know whether you followed the link on the Add-ons page about this, but if not, the following article has more information: https://support.mozilla.org/questions/1099817 Kaspersky has not yet gotten its extensions signed by Mozilla, so the signing requirement is blocking them. You can make a temporary exception to the signing requirement -- this is global for all extensions, there's currently no way to only make an exception for specific extensions. (1) In a new tab, type or paste '''about:config''' in the address bar and press Enter/Return. Click the button promising to be careful. (2) In the search box above the list, type or paste '''xpin''' and pause while the list is filtered (3) Double-click the '''xpinstall.signatures.required''' preference to switch it from true to false -- note that this is for '''Firefox 43 only'''

it worked! Thanks very much.