In order inform the user of possible conflicts, I'd like to have my add-on check if another add-on is installed and enabled. If so, I can disable either it or my own at the user's bequest:

function disableExtension(id) {
    var man = Components.classes["@mozilla/extensions/manager;1"];
    if (man) {
        man = man.getService(Components.interfaces.nsIExtensionManager);
    }
    if (man) {
        man.disableItem(id);
    } else {
        Components.utils.import("resource://gre/modules/AddonManager.jsm");
        AddonManager.getAddonByID(id, function(addon) {
            addon.userDisabled = true;
        });
    }
}

But I first, of course have to check if a certain other add-on is installed. Presently, I do this as follows:

if (Application.extensions) {
    // Gecko 1.9.2 and older
    ext = Application.extensions.get(id);
    if (ext) {
        // TODO check if extension is also enabled
        disableExtension(id);
    }
} else {
    // Gecko 2.0.0 and newer
    Application.getExtensions(function(extensions) {
        ext = extensions.get(id);
        Components.utils.import("resource://gre/modules/AddonManager.jsm");
        AddonManager.getAddonByID(id, function(addon) {
            if (!addon.userDisabled) {
                disableExtension(id);
            }
        });
    })
}

The code for Firefox 4 (the else-statement) works fine. For older versions of Firefox (3.5 and older), I can't for the life of me figure out how to determine if the extension is in fact installed.

Does anybody know how to do this?

In order inform the user of possible conflicts, I'd like to have my add-on check if another add-on is installed and enabled. If so, I can disable either it or my own at the user's bequest:

function disableExtension(id) {
    var man = Components.classes["@mozilla/extensions/manager;1"];
    if (man) {
        man = man.getService(Components.interfaces.nsIExtensionManager);
    }
    if (man) {
        man.disableItem(id);
    } else {
        Components.utils.import("resource://gre/modules/AddonManager.jsm");
        AddonManager.getAddonByID(id, function(addon) {
            addon.userDisabled = true;
        });
    }
}

But I first, of course have to check if a certain other add-on is installed. Presently, I do this as follows:

if (Application.extensions) {
    // Gecko 1.9.2 and older
    ext = Application.extensions.get(id);
    if (ext) {
        // TODO check if extension is also enabled
        disableExtension(id);
    }
} else {
    // Gecko 2.0.0 and newer
    Application.getExtensions(function(extensions) {
        ext = extensions.get(id);
        Components.utils.import("resource://gre/modules/AddonManager.jsm");
        AddonManager.getAddonByID(id, function(addon) {
            if (!addon.userDisabled) {
                disableExtension(id);
            }
        });
    })
}

The code for Firefox 4 (the else-statement) works fine. For older versions of Firefox (3.5 and older), I can't for the life of me figure out how to determine if the extension is in fact installed.

Does anybody know how to do this?

• javascript
• firefox
• firefox-addon
• xp

• The only thing that es to mind is running through extensions.ini and looking for the extension's getInstallLocation(), but I don't like that approach at all. – Paul Lammertsma Commented Nov 28, 2010 at 3:29

2 Answers 2

The answer was trivial; I had overlooked the enabled attribute for extIExtension.

I resolved it as follows:

var ext;
if (typeof Application != 'undefined') {
    if (Application.extensions) {
        // Gecko 1.9.0 - 1.9.2
        ext = Application.extensions.get(id);
        if (ext) {
            if (ext.enabled) disableExtension(id);
        }
    } else {
        // Gecko 2.0.0 and newer
        Application.getExtensions(function(extensions) {
            ext = extensions.get(id);
            Components.utils.import("resource://gre/modules/AddonManager.jsm");
            AddonManager.getAddonByID(id, function(addon) {
                if (!addon.userDisabled) {
                    disableExtension(id);
                }
            });
        })
    }
} else {
    // Gecko 1.8.0
    var extMgr = Cc["@mozilla/extensions/manager;1"].getService(Ci.nsIExtensionManager);
    if (extMgr) {
        ext = extMgr.getItemForID(id);
    }
    var extMgrDs = extMgr.datasource;
    if (extMgrDs) {
        var rdfSvc = Cc["@mozilla/rdf/rdf-service;1"].getService(Ci.nsIRDFService);
        if (rdfSvc && ext) {
            var source = rdfSvc.GetResource("urn:mozilla:item:" + ext.id);
            var property = rdfSvc.GetResource("http://www.mozilla/2004/em-rdf#isDisabled");
            var target = rdfSvc.GetLiteral("true");
            var disabled = extMgrDs.HasAssertion(source, property, target, true);
            if (!disabled) {
                disableExtension(id);
            }
        }
    } else if (typeof className != "undefined") {
        // Opens the add-on window
        BrowserOpenAddonsMgr();
    }
}

Where disableExtension() is:

disableExtension: function(id) {
    var man = Components.classes["@mozilla/extensions/manager;1"];
    if (man) {
        man = man.getService(Components.interfaces.nsIExtensionManager);
    }
    if (man) {
        man.disableItem(id);
        restart();
    } else {
        Components.utils.import("resource://gre/modules/AddonManager.jsm");
        AddonManager.getAddonByID(id, function(addon) {
            addon.userDisabled = true;
            restart();
        });
    }
}

And restart() is:

restart: function() {
    var appStartup = Components.classes["@mozilla/toolkit/app-startup;1"];
    if (appStartup) {
        appStartup = appStartup.getService(Components.interfaces.nsIAppStartup);
    }
    if (appStartup) {
        appStartup.quit(appStartup.eAttemptQuit | appStartup.eRestart);
    } else if (typeof Application != 'undefined') {
        if (Application.restart) Application.restart();
    }
}

This hasn't been tested on Firefox 1.0-1.5, but works on:

• Firefox 4.0b7
• Firefox 3.6
• Firefox 3.5
• Firefox 3.0
• Firefox 2.0

Credit for helping me out goes to Atte Kemppilä.

Very informative write-up.
Note that you can use the "enabled" attribute for Gecko 2 as well. This makes the code somewhat simpler.

   if (Application.extensions) {
        // Gecko 1.9.0 - 1.9.2
        ext = Application.extensions.get(id);
        if (ext) {
            if (ext.enabled) disableExtension(id);
        }
    } else {
        // Gecko 2.0.0 and newer
        Application.getExtensions(function(extensions) {
            ext = extensions.get(id);
            if (ext.enabled) disableExtension(id);
        });
    }

For best practice you can of course move the repeated code to an external function.