Service extension warning

Recently I started getting the above warning indicating that a "service extension" differs from the previously opened version. However, the dialog does not indicate which extension it is or what application it is linked to. Thus I always opt for not opening it.

If I reboot my MacBook the problem goes away for a couple of hours. But eventually it comes back. It happens more often when I am browsing, regardless of whether I am using Safari or Firefox.

Any you can provide will be much appreciated.