Posted from another user:
I run Windows 10 Pro 64-bit build1510 since March 29, 2016. Since some days Agent Ransack didn't start anymore when I press CTRL-F or F3 in an Explorer window. Instead, the built-in search tool was activated always.
Fortunately, this post provided the fix. In my case, I found the Agent Ransack add-on as "new" instead of "active" in the Internet Explorer add-on manager. I fixed that setting and rebooted. Now A.R. works again.
The reason why the shell integration was disabled is not clear for me. Maybe a system update disabled the add-on (I would appreciate if other users would confirm this opinion), or I somehow touched a bad combination of keys on my keyboard? At least I am sure I never re-installed, re-configured or updated A.R. since March 29.