When Kate is already open, and in Firefox I press Ctrl-U to open the web page in the assigned external text editor (Kate), the web content opens in a second Kate session.

I want to use the current session only. I'm an MDI kind of person. :)

Editing the Firefox preferences to "kate --use" then causes Firefox to open the web page content in the Firefox viewer rather than Kate.

All of my kate related *.desktop files are set to kate --use.

Any ideas how to fix this?

Darrell