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Three methods to force add-on compatibility in Firefox

You may have read in our announcement post about the latest beta version of Firefox 3.6 coming from Mozilla developers. changed the plugin compatibility parameter in the Firefox web browser.

Therefore, this article describes three different ways to force add-on support in the upcoming Firefox 3.6 browser.

It should be noted that forcing compatibility may not always produce the desired result. It will work fine if the developer has not yet updated the plugin to be compatible with the latest version of Firefox. However, it will not work, or will cause errors, if the add-on uses features that have changed in the latest version of Firefox.

Note: The article describes methods that worked in classic Firefox. These methods no longer work in new versions of the web browser. Firefox users can run the Add-on Compatibility Report however, to report to Mozilla about add-ons that no longer work properly.

Method 1: Nightly Test Tools

install firefox plugin

The Nightly Tester tools have been designed for Firefox developers who want to test (their) add-ons on new versions of the web browser.

This Firefox addon forces compatibility so that the addon can be installed even if the compatibility information says otherwise. This is a very simple and easy way. Firefox users with this add-on usually need to download the add-on that is not compatible with their version of Firefox from the add-on page that shows all versions to download (the latest downloaded version usually becomes inactive if the user’s version of Firefox it is not compatible).

Nightly Tester Tools will display the following window if it is determined that the plugin is not compatible with the version of Firefox:

force compatibility plugin

It is also possible to force compatibility for all addons that are already installed in the addon manager in Firefox.

firefox override compatibility

Nightly Tester Tools is available on the Mozilla Firefox website.

Method 2: Edit Firefox Settings

This is the method that the browser developers have changed. It impacts only Firefox 3.6 beta 3 and newer, which means that most users will not have experienced the changes yet.

Before that version it was possible to create a new extensions.checkCompatibility boolean parameter in the Firefox configuration and set it to false to be able to install all Firefox addons regardless of their compatibility.

check the compatibility of Firefox extensions

This was changed by the Firefox developers so it is now necessary to add a version to the parameter. What this means is that from Firefox 3.6 beta 3 onwards it is only possible to override support for a specific version of Firefox. The times of changing a parameter once are therefore a thing of the past.

The Firefox user must add the browser version to the parameter, for Firefox 3.6 beta 3 it would be extensions.checkCompatibility.3.6b, for Firefox final 3.6 extensions.checkCompatibility.3.6 and so on.

The advantage of this method is that it does not require the user to install a plugin to force compatibility. However, it has become more complicated with this change. On the other hand, it does not provide the same level of customization that Nightly Tester Tools offer (the parameter enables all plugins automatically and the user would have to disable or uninstall the plugin to stop using it).

Method 3: Edit Firefox Addon File Directly

Now this method was popular when Firefox 1 became more popular. Nowadays it’s more of a nice-to-know method than a practical one, since the other two methods should be all that is needed to make a plugin compatible with the internet browser.

Users must first download the plugin on their computer system. The plugin is an xpi file which must then be extracted with a program such as 7-zip. This will extract all the plugin files, including a file called install.rdf in the root directory.

Open that file in a text editor and find the following two lines:


These two parameters define the compatibility limits of the plugin. Change versions (usually the maxVersion is all that needs to be changed) for the version of Firefox to be included. After that create a new zip file with the updated content and rename the extension from zip to xpi. Install the edited plugin in the web browser by dragging and dropping it onto its interface.

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