The amount of Page Rank (or “link juice”) passed by Google through a link is inversely proportional to the number of links on a page. All else being equal, the best way to increase the juice flowing through a link is to remove some of the other links on the page.

Counting the links on a page is therefore a useful tool for understanding how link juice passes through a page. There used to be a great link-counting plug-in for Firefox, but its author stopped updating it a long time ago, and it stopped working as of Firefox 3.

Benj Arriola of SEOreligion.com updated the add-on to work with Firefox 3, but his version expired as of 3.5.1. You can still download Benj’s modified XPI here if you need to.

The link-counting code still runs fine under Firefox 3.5.X, but won’t install without modification. Here are step-by-step instructions for modifying the add-on to work with FF 3.5.3 or later. For OS X:

1. Change the XPI file’s extension to .zip.
2. Double-click the file; OS X will recognize it as a ZIP archive and unpack it.
3. Open the resulting folder to show the archive contents.
4. Open the install.rdf file in a text editor.
5. Find the “EM:maxVersion” line and change the value to something greater than the current FF version, e.g. 3.7.5.*:
   em:maxVersion="3.7.5.*" />
   You might wish to increment the version number too, e.g. to 1.3.1.
6. Save the file.
7. In the Finder, select the modified install.rdf file and the other four items next to it (chrome.manifest, defaults folder, todo.txt, chrome folder).
8. CTRL-click to show the contextual menu for the Finder, and select the “make archive” item (or “Compress 5 items” depending on your OS version).
9. Rename the resulting .zip file to LinkCounter.xpi. You may need to do this within the archive’s Get Info window. Make sure the file has an .xpi extension, or Firefox won’t accept it.

To install the modified add-on:

1. Uninstall any previous version of the plug-in, if necessary; then restart Firefox.
2. Open the Add-Ons window.
3. Drag the new LinkCounter.xpi file from the desktop onto the Add-Ons window.
4. Confirm installation when prompted.

If you use Windows, the basic steps for modifying the XPI are the same, although the OS may not do the ZIP creation for you (not sure).