I am using Firefox 4.0.1 on my 11.04 Ubuntu system. I have added one plugin for Firefox called Pencil.It which isn't working. How to solve that?
Pencil.it doesn't support Firefox 4, it only works with Firefox 3.0b3 - 3.6.*. There hasn't been any development since June, so it's impossible to estimate when support will land if ever.
You could try to bypass the test, but make sure you backup your bookmarks etc as things might get ugly.