In Ubuntu PDF files by default are opened in a separate PDF viewer.However,it would be better to view the online PDF files in web browser.Following shows how to get online PDF embedded within the Firefox window.

First,open terminal from Application->Accessories->Terminal to type this command to install Mozplugger and Evince:

sudo apt-get install evince mozplugger

Edit the Mozplugger config file by:

gksudo gedit /etc/mozpluggerrc

find out following section:

application/pdf:pdf:PDF file
application/x-pdf:pdf:PDF file
text/pdf:pdf:PDF file
text/x-pdf:pdf:PDF file
ACROREAD()
repeat noisy swallow(kpdf) fill: kpdf “$file”
repeat noisy swallow(Xpdf) fill: xpdf -g +9000+9000 “$file”
repeat noisy swallow(okular) fill: okular “$file”
GV()
repeat noisy fill exits: evince “$file”

replace above with following code if you want to use xpdf PDF viewer within the Firefox:

application/pdf:pdf:PDF file
application/x-pdf:pdf:PDF file
text/pdf:pdf:PDF file
text/x-pdf:pdf:PDF file
repeat noisy swallow(Xpdf) fill: xpdf “$file”
ACROREAD()
repeat noisy swallow(kpdf) fill: kpdf “$file”
repeat noisy swallow(okular) fill: okular “$file”
GV()
repeat noisy fill exits: xpdf “$file”

Or if you would like the Evince PDF viewer replace with this:

application/pdf:pdf:PDF file
application/x-pdf:pdf:PDF file
text/pdf:pdf:PDF file
text/x-pdf:pdf:PDF file
repeat noisy swallow(evince) fill: evince “$file”
ACROREAD()
repeat noisy swallow(kpdf) fill: kpdf “$file”
repeat noisy swallow(Xpdf) fill: xpdf -g +9000+9000 “$file”
repeat noisy swallow(okular) fill: okular “$file”
GV()
repeat noisy fill exits: evince “$file”

Close and save changes.Logout and back in,then open Firefox and try to view a PDF file.
Original text:http://sprayfly.com/2010/01/15/view-pdf-files-inline-in-firefox-on-ubuntu-karmic-9-10/