Hello, in this tutorial I'll explain how you make old firefox addons compatible with newer versions of FireFox.

-Step 1-
Search the addon you want on
https://addons.mozilla.org/firefox/

Pick the addon you want, for this tutorial I'll use Add 'N Edit Cookies.
You'll notice if you're using the newest version of FireFox that you aren't able to install it.


Step 2-
Start Internet Explorer or another browser. Go to the page of the addon and download it. You'll notice the file is a .xpi file.



-Step 3-
Change the extension from .xpi to .zip , you'll notice the file is now a archive.

-Step 4-
Open the archive with Winrar , Winzip or another program to view archives.
When you're viewing the archive you'll see serveral files the only 1 we need will be install.rdf. Extract install.rdf to your desktop or another place.



-Step 5-
Right mouse click on install.rdf and edit it. I'll use Notepad++

-Step 6-
Now hit CTRL+F (Search) and search for maxVersion. You'll see that the maxversion = 3.0. Change the 0 to 5. Hit CTRL + S (Save).



-Step 7-
Now drag the file back to the archive and replace it with the old install.rdf .
Change the file extension back from .zip to .xpi .

-Step 8-
Start FireFox and drag the .xpi file the FireFox and you'll see the addon install window. Install the addon and restart FireFox.