This is easy to reproduce. Right clicking an Adobe Flash plug-in causes Firefox to hang until npviewer.bin is killed. Toggling the value of dom.ipc.plugins.enabled as suggested by ToniTC works.
Not being able to click on built-in dialogues is probably a separate issue. To work around the bug, you have to disable compiz (no special effects under appearance settings).
This is easy to reproduce. Right clicking an Adobe Flash plug-in causes Firefox to hang until npviewer.bin is killed. Toggling the value of dom.ipc. plugins. enabled as suggested by ToniTC works.
Not being able to click on built-in dialogues is probably a separate issue. To work around the bug, you have to disable compiz (no special effects under appearance settings).