Mac command line parsing doesn't work

I'd really like to be able to use the wonderful "Command Line Support" plugin, but it (and other command line options) don't work on OSX. Specifically, running /Applications/Songbird.app/Contents/MacOS/songbird -no-remote -play gives the standard "there is already another songbird instance running" dialog.

I did some digging, and it looks like there is a specific "macCmdLineFwd.xul" set as the "browser.chromeURL" user preference. This all looks like it's supposed to take command line arguments and forward them to the active instance, but I can't get that to work whatever I try. I know command line stuff with xulrunner on mac is difficult (I've spent all afternoon trying to figure out what's going on), but this extension is absolutely vital until we get another way to set global keyboard shortcuts.

version: 1.2.0 - intel mac