Compact Databases over the LAN?

Today I tried ticking "Compact Databases" for my Firefox and Thunderbird applications and as I watched it work, I noticed that the program was working on databases that were long-ago saved-out (backed-up) to a couple of my Network drives!? It made the "Compact Databases" progress very very slow, given I suppose that my Comodo Internet Security (firewall, executable, virus checking) was watching the network activity, and in fact I aborted the "clean" when it seemed to get stuck on an old Tbird backup out on a NAS.

Where would CCleaner get the information/knowhow to leave this computer that it's running on, and the profiles FF and TBird are using on this PC, and go-out onto the LAN and try to compact old (backed-up) profiles I may have saved out there? I looked in the Registry and could find no clues. Is there any way to stop this behavior?