You can't enclose a Filemaker variable in quotes and then expect the value of the variable to be substituted in place of the variable's name.
SendEvent [ open document/application : "cmd.exe /C " & Settings::htmleditor& " " & Quote ($appfile) ] [Bring application to foreground]
Thank you very much. Of course this is what I should have done after staring at it for several hours. I also was tripped up by thinking I needed the closing quote after I had put in the FM datafield. You are the best.