Rated 5 out of 5 stars

This addon works fine in 4, you just need to tell firefox it is compatible with ver 4.
To do this
Save the file as an xpi on your hard drive
Rename the ending of the file from xpi to zip
Open file in winzip or winrar whichever you have
Double click on install.rdf and select to open with notepad
Once notepad is open scroll down until you find the line
<em:maxVersion>3.6.x</em:maxVersion>
and change this to
<em:maxVersion>6.01a</em:maxVersion>
Save the file and close notepad, you will see a box on top of winrar asking to update the file, say yes, close winrar/winzip
Rename the file back from .zip to .xpi
Double click on the xpi and if necessary select firefox to open it with and then it will add into firefox without problems and you can then add to your toolbar :)
It works fine for me :D