Did you use the method to create a new Boolean pref?

• network.protocol-handler.expose.rdp = false

That should make Firefox ask which application to use when you try to open such a link.

Yes, I did exactly that. Is it necessary to restart browser after that? (I tried it immediately and after restart and nothing). Can somebody try it in Linux? I tried Iceweasel 26.0 from Debian and also downloaded Firefox tar - the same result, but I tried it only on my laptop.. Can it be my linux issue? I assume not.

I have created this pref and used the DOMi to created a rdp://example.com link.

<a href="rdp://example.com">rdp</a>

Clicking this link immediately showed a pop-up to select which application to use.

Make sure that there aren't any other rdp prefs left from other experiments.

You can also check the mimeTypes.rdf file for references to this protocol.

• http://kb.mozillazine.org/mimeTypes.rdf
• http://kb.mozillazine.org/File_types_and_download_actions#Resetting_download_actions

Now I have the point. When I create <a href="rdp://example.com">rdp</a> html file, it is asking for application. But when I put rdp://example.com to the URL address bar, I get ... the protocol (rdp) isn't associated with any program. Now I try it with thunderlink://, because it was my first "protocol" I wanted to register.

So final result and recapitulation.

I was trying to register new protocol (thunderlink, rdp etc) and I was testing it with workflowy web todo list. I think that workflowy's javascript opens links in new tab just like when you open new tab and paste URL into it. But it will never trigger application selection (even when you have network.protocol-handler.expose.protocol = false).

I think that shoud be concidered as firefox bug.

I used woraround - see cor-el's advice - created html file with new protocol hyperlink, click it and the selection popup appeared.

After that, all clicks (even in workflowy) open the right app I wanted.