when I click download in youtube this is how Firefox tells me as the whole youtube page disappears- Firefox doesn't know how to open this address, because one of the following protocols (ummy) isn't associated with any program or is not allowed in this co

Please help me with the above issue- Firefox says this just after I Click the save from Net download button in Youtube but recently I have been using it without any complications.

Firefox doesn't know how to open this address, because one of the following protocols (ummy) isn't associated with any program or is not allowed in this context.

You might need to install other software to open this address.