I was thinking about how to open a PDF file inside Firefox on Ubuntu, like the Acrobat plugin do on Windows, but using Evince.

So I “googled” about Evince and Firefox and found it quickly in the Lâmpada Azul site. Altought it has many steps, I used only the first and it worked very well. You have only to install the mozplugger package:

sudo aptitude install mozplugger

Alright. It may works now.