Udo's Techblog

Here’s the thing: for good reason, the Firefox team forced every plugin specify the exact version it is compatible with. So, for example, say FireFTP claims compatibility with Firefox versions 3.0 through to 3.5b2 (or whatever). Now, following this example, once you install Firefox 3.5b3, it’s over. Firefox will disable the plugin and you’ll have to wait until the developer of the plugin brings out an update that makes it work again.

The screwed-up mechanism here is in Firefox’ add-on manager which refuses to let your plugin run, even if you really really want it to. For your own protection, of course. You’re not allowed to override this decision, even if you’re using an add-on that is no longer being maintained by its developer. I can only assume this fine piece of UI philosophy is – like so many bad ideas in the world – somehow inspired by Java, or possibly by one of its even more authoritarian frameworks, but I digress.

Anyway, here’s how you can fix it yourself. But first consider yourself warned: your plugin may very well not work or if it does, there may be some hidden malfunction just waiting for the right moment to erase your hard drive, melt down your computer into a puddle of toxic waste and then implode the entire internet which could make you liable for billions of dollars in damages. Having said that, let’s move on:

Finding the “extensions” directory
On OS X, Firefox add-ons are kept in your user directory, the path would be something along these lines:

/Users/(your username)/Application Support/Firefox/Profiles/

Now, in this folder, you’ll see a cryptic folder that’s called something like “3245hjg.default”. Open it.

Here you’ll find a file called “extensions.rdf”, open it with a text editor and keep it open for later. Inside the same folder you’ll find another folder called “extensions”, open it.

Find the appropriate add-on
You have now reached the stage where the fun really starts. See, most plugins don’t use a human-readable folder name, but instead are called something ridiculous like

{a7c6cf7f-112c-4500-a7ea-39801a327e5f}

That’s called a GUID, or globally unique identifier; if you’re interested in this number, ask your local COM or Java developer for a more in-depth, undoubtedly fascinating diatribe, but let’s move on for now. To see what GUID your favorite add-on has, go to the text editor window containing the “extensions.rdf” file from the previous paragraph. Do a text search for the name of your plugin. You should find something like this:

<RDF:Description RDF:about="urn:mozilla:item:{a7c6cf7f-112c-4500-a7ea-39801a327e5f}"
                   NS1:installLocation="app-profile"
                   NS1:version="1.0.4"
                   NS1:optionsURL="chrome://fireftp/content/preferences.xul"
                   NS1:iconURL="chrome://fireftp/skin/icons/logo32.png"
                   NS1:name="FireFTP"

I have marked the GUID associated with FireFTP in bold here, you’ll just do a search on your own and find your add-on’s GUID. Now go to the Finder window with the “extensions” folder and navigate to the directory of the same name as the GUID you found. Open it.

Cracking the version barrier
You should now be inside the extension’s folder. There is a file in there called

install.rdf

Open it. Inside you’ll find a passage that looks like this:

        <em:minVersion>3.0</em:minVersion>
        <em:maxVersion>3.5b2</em:maxVersion>

Change the value of maxVersion to (or beyond) your current Firefox version. Save the file, restart the Fox. You should now be able to open the add-on manager and re-enable the plugin.

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