I'm also not able to send to GPS on a Mac with 10.7.3, but I am on a Mac with 10.5.8. I think this is because it is looking for the plug-in in the wrong place from what I can till looking at this./Users/name/Library/Application Support/Firefox/Profiles/ifa67tlz.default/extensions/{195A3098-0BD5-4e90-AE22-BA1C540AFD1E}/plugins/GarminGpsControl.plugin/Contents/Resources/GPX10toGPX11.xsl. There is no Library folder in the users folder for 10.7.3 but is in 10.5.8. The Library folder in 10.7.3 is located in the hard drive. The file GarminGPSControl.plugin is now located in hard drive/Library/internet Plugins.