Can't be sure of that but you may be right. I can't remember all the fiddling I may have done there (and some memory is quite confusing, years ago, I used to use some plugin to let me use something like pmidi inline but I've forgotten how that worked) and am not even sure where along the line vlc became an option for this on both Firefox and Chromium but can be sure that I used Edit/Preferences/Applications on Firefox to make the midi editor (Rosegarden) an option.