Comment 46 for bug 239952

It worked, thanks, and I must say the Mac version seems completely broken compared to the 2 other ones :(

mimeSvc.getFromTypeAndExtension('application/postscript', 'ps') gives a handler with extensions list ['eps']
mimeSvc.getFromTypeAndExtension('application/postscript', null) gives a handler with extensions list ['eps']
mimeSvc.getFromTypeAndExtension('application/postscript', 'eps') gives a handler with extensions list ['eps']
mimeSvc.getFromTypeAndExtension('application/postscript', 'ai') gives a handler with extensions list ['ai', 'ps', 'eps'];
mimeSvc.getFromTypeAndExtension('application/postscript', 'foo') gives a handler with extensions list ['ps', 'eps', 'ai'];

The only good point is that it's consistent with getPrimaryExtension:
mimeSvc.getPrimaryExtension('application/postscript', null) is 'eps';
mimeSvc.getPrimaryExtension('application/postscript', 'eps') is 'eps';
mimeSvc.getPrimaryExtension('application/postscript', 'ps') is 'eps';
mimeSvc.getPrimaryExtension('application/postscript', 'ai') is 'ai';
mimeSvc.getPrimaryExtension('application/postscript', 'foo') is 'ps';