Firefox collides with Windows Explorer

Hi,

I'm new here, and not aware of group do's and don'ts....

Since a few months I have problems downloading any file from any 
website. The browser simply completely disappears on the moment I start 
navigating to the folder where I want the file to land.

No problem in Google Chrome

Yesterday I wanted to upload a file to our Joomla website using the 
Phoca Download Plugin to make it available. This process also involves 
navigating an explorer window to the folder where my file resides, and 
again the complete browser vanished.

Again, no problem in Google Chrome.

Firefox is as always up to date. I have uninstalled it and then 
reinstalled, but the problem did not go away.

Please, help!

Leo