Hack Extension Files to Make Them Version-Compatible for Firefox

A well known drawback in using Firefox is the problem with extension compatibility when a new major version is released. Whether it is for a new extension that you are trying for the first time or an old favorite we have a way to get those extensions working for you again.
There are multiple reasons why you might want to choose this method to fix a non-compatible extension:

• You are uncomfortable with tweaking the “about:config” settings
• You prefer to maintain the original “about:config” settings in a pristine state and like having compatibility checking active
• You are looking to gain some “geek cred”

Keep in mind that most extensions will work perfectly well with a new version of Firefox and simply have the “version compatibility number” problem. But once in a while there may be one that needs to have some work done on it by the extension’s author.
The Problem
Here is a perfect example of everyone’s least favorite “extension message”. This is the last thing that you need when all that you want is for your favorite extension (or a new one) to work on a fresh clean install.
Note: This works nicely to “replace” non-compatible extensions already present in your browser if you are simply upgrading.

Hacking the XPI File
For this procedure you will need to manually download the extension to your hard-drive (right click on the extension’s “Install Button” and select “Save As”). Once you have done that you are ready to start hacking the extension.

For our example we chose the “GCal Popup Extension”. The best thing to do is place the extension in a new folder (i.e. the Desktop or other convenient location) then unzip it just the same way that you would with any regular zip file.
Note: HTG reader Dante pointed out that if you do not have a third party zip utility such as IZArc or 7-Zip installed changing the “.xpi” file extension to “.zip” will allow you to use Windows integrated zip software to unzip the file.
Once it is unzipped you will see the various folders and files that were in the “xpi file” (we had four files here but depending on the extension the number may vary). There is only one file that you need to focus on…the “install.rdf” file.
Note: At this point you should move the original extension file to a different location (i.e. outside of the folder) so that it is no longer present.

Open the file in “Notepad” so that you can change the number for the “maxVersion”. Here the number is listed as “3.5.*” but we needed to make it higher…

Replacing the “5” with a “7” is all that we needed to do. Once you have entered your new “maxVersion” number save the file.

At this point you will need to re-zip all of the files back into a single file. Make certain that you “create” a file with the “.zip file extension” otherwise this will not work.

Once you have the new zip file created you will need to rename the entire file including the “file extension”. For our example we copied and pasted the original extension name.

Once you have changed the name click outside of the “text area”. You will see a small message window like this asking for confirmation…click “Yes” to finish the process.

Now your modified/updated extension is ready to install.

Drag the extension into your browser to install it and watch that wonderful “Restart to complete the installation.” message appear.

As soon as your browser starts you can check the “Add-ons Manager Window” and see the version compatibility numbers for the extension. Looking very very nice!

And just like that your extension should be up and running without any problems.

Conclusion
If you are looking to try something new, gain some geek cred, or just want to keep your Firefox install as close to the original condition as possible this method should get those extensions working nicely for you again.