Rated 5 out of 5 stars
This WILL work on FF 4.0 with some help. The easy way is to install 7-ZIP (Google it), then download add-on with IE or an older version of FF. Associate the .XPI extension with 7-ZIP by double clicking it, when Windows complains about no association tell it 7-ZIP. With the XPI open RIGHT click on the install.rdf and choose EDIT. Find the line "<em:maxVersion>3.6.*</em:maxVersion>" and change the 3.6 to 4.0, close notepad, save the file, 7-ZIP then prompts to save the edited file in the archive. Say YES. Open FF, go to Add-Ons and just drag and drop the XPI file on the add-ons dialog or choose install from file from the menu. Restart FF, add the anchor button to whatever toolbar you want and enjoy.