Hello,
I am using an older version of Lazarus (see signature) so maybe this feature has already been implemented, in that case, never mind
The menu Run->Run Parameters shows a dialog box, one of the fields there is "Command line parameters (without application name)", since quite often the parameter is a filename, it would be very nice if it were possible to drag and drop a file from Windows Explorer (or whatever equivalent is in another O/S) and have the file name appear in the box. It would be particularly nice if the drop handler inspected the filename for spaces and added the necessary quotes at the beginning and end of it.
Another possibility would be to add a "..." button, like the ones for "Host application" and "Working directory" to the "Command line parameter etc" to select a filename.
Either one can occasionally be quite a time saver.