How to modify Add-ons to work with newer versions of Firefox/Thunderbird.

Firstly let me say this, there may be a reason why your favourite add-on is only listed as working with an older version of FF or TB, so if modifying the max version number and running the Add-on eats your Hard Drive and re-arranges your keyboard letters, don't say I didn't warn you.

In saying that, in the case of the Firefox Growl/GNTP plug-in it is simply that the max version is set to 4.0.* and we are now at 5.0.0. Its an easy fix, here's how. First we we deal with an existing install of the Add-on, if you have not installed it yet see section 2 below.

Section 1 - Update to new FF version with Add-on already installed.

1. Shutdown Firefox (or Thunderbird )
   
   
2. Find the Add-on directory, on Windows 7 x64 for Firefox its C:\Users\YourUserName\AppData\Roaming\Mozilla\Firefox\Profiles\RandomNumber.default\extensions or for Thunderbird C:\Users\YourUserName\AppData\Roaming\Thunderbird\Profiles\RandomNumber.default
   
   
3. Look for the folder of .xpi file you want, we get lucky for the Growl plugin as its called growlgntp@brian.dunnington.xpi , .xpi files are simply re-named .zip archives, so you should be able to right click and open as an archive (I suggest 7zip if you don't have an archive manager). If you cant see the name of the plugin you want you will have to check each file / folder and read the install.rdf file, look for the em:name=  tag for the Add-on name. (In 7zip you can right click the install.rdf and select edit to open the file in notepad)
   
   
4. Once you have found the right file or folder, in that same install.rdf file look for the em:maxVersion="4.0.*" tag, as you can see at present its set to 4.0.* in Growl/GNTP, change it to 5.0.*
   If in a folder, just save the file and close once the changes are made, if you have used 7zip / edit when you close the notepad window it will ask to update the archive, select yes.
   
   
5. Restart the app, if you haven't updated yet do so and you should not see the plugin in the To Be Disabled list. If you have already updated prior to making the changes go into the Add-ons menus and re-enable.

Section 2 - New Add-on to be installed.

1. Go to the Add-ons page and right click on the "Add to Firefox" button, select "Save Link As" and download the .xpi file, dont let Firefox try to install the Add-on yet.
2. Navigate to the downloaded .xpi file. .xpi files are simply re-named .zip archives, so you should be able to right click and open as an archive (I suggest 7zip if you don't have an archive manager).
3. Once you have the .xpi archive open look for the install.rdf file, this is a text file that you can edit (In 7zip you can right click the install.rdf and select edit to open the file in notepad), look for the em:maxVersion="4.0.*" tag, as you can see at present its set to 4.0.* in Growl/GNTP, change it to 5.0.*and save the changes back to the archive.
4. Right click on the fixed .xpi file and open with FireFox (or ThunderBird), you should now be installing the Add-on.

How to fix Firefox Growl/GNTP plug-in.
Fix Firefox Growl