suggestion: default editor

can add an option: default editor? for those files that are not set in file associations box, always open with this default editor.

[psxc]

You already got this in Options -> File Associations. Granted, not default, but do you have all that many different filetypes that it's impossible to add them there?

[Ethanol]

To try and satisfy your request, I found a workaround:

Option -> File Associations (or whatever it is in your version).

Add an extension .*

Choose the program to view/edit with.

Unfortunately, Flash doesn't have a priority for extensions, so I think it depends on where this (.*) is in the list as to whether the file will open with this "default" editor.