How do I set firefox to open an app without asking the user?

I have a server application that posts a custom mime file of type "application / x-optibase".

Firefox will prompt the user to save or open the file and if the user clicks on open the correct launch applications, so I believe the mimeType.rdf is configured correctly

I told: config and set

browser.helperApps.neverAsk.openFile for app / x -optibase

and

browser.helpApps.alwaysAsk.force - false

According to minimal documentation, this should allow the app to automatically open when the user uploads the file, but it doesn't seem to work.

Any ideas?

Thank.