Please describe the problem:
I am not sure if this is the right category for this annoyance.
Problem: Say I do not want the entry Firefox in the "Open with" menu for html files and attempt to remove it.

Steps to reproduce:
1. Attempt to remove Firefox from the list for html documents (using an Ubuntu installation)
2. Observe the results


Actual results:
Nothing happens in the properties dialog; the disabled Firefox entry in the Gnome menu is restored (?).

Expected results:
Remove entry from "open with" menu.

Does this happen every time?
Yes.

Other information:
Why do I want to do this? I use Epiphany but want to keep Firefox installed so to not break the metapackage that is needed for updates on my Ubuntu installation. Maybe the developers feel that this is a feature to prevent users from removing important entrys; then however the "remove button" should at least be greyed out or better implement a "restore to default" button.