How to install Add-on for Firefox without caring version compatibility?

Yersterday Firefox has released his beta 5 for version 3. I’m using FF 3 beta 4 which I write a review before and this update was automatically made, so I am forced to use the newest version. And as consequence my Adblock Plus add-on doesn’t work anymore in this new version. But I would like to use it anytime when I surf net so that I do not have to see the bad advertisements on web. So I try to find a way to handle with this problem…

First I go to the development site of Adblock Plus to download the latest version of this add-on, try to install it on FF 3 beta 5 but… naturally I doesn’t work. A message was popped up telling that an incompatible version was happened

Error Message

So I click right on the link and download it to my machine to research later. The extension of file is a .xpi extension, I rename it to .zip so that I can see what kind of files are in this package. After renaming I extract all files to a directory.


You see there are 2 files relating with the install process of Adblock Plus. Because of the incompatible version I believe that there must be a constant variable containing the version of Firefox so that Adblock Plus can check its compatibility. So I opened up the javascript file install.js and search with the keyword “3” for the version of FF. I found some but they are not related to version of FF.

Then I opened the install.rdf file with Notepad. Notepad is really a strongest tool which I see. For file with unknown extension I usually use it to open and it can read 80% of the cases. I search again with the keyword “3” and found an interesting XML tag 3.0b5pre .

Max Version

I just change it to 3.0b6, save file and zip all files again, rename it to .xpi extension. Try to install and at last I have my Adblock Plus add-on again with my newest Firefox.

Although this method works in some cases but in most of cases it doesn’t work because of the invalid signing of the add-on. You will receive an error “Signing could not be verified”. To handle this problem we need to add some new options into configuration of Firefox.

In address bar of Firefox, type about:config and enter.

* Click button “I’ll be careful, I promise” otherwise we can not access the configuration of Firefox.
* Right-click anywhere. Choose New>Boolean.


* Make the name of your new config value extensions.checkCompatibility and set it to false.

Set Name

* Make another new boolean pair called extensions.checkUpdateSecurity and set the value to false.
* Restart Firefox.

After adding these values you can install any add-on which you like without caring of version compatibility. However when you access Firefox add-on website, you can not install them because Firefox checks the version to allow which add-ons can be installed.


To activate this install we go to configuration site again through about:config. Filter to find this key “general.useragent.extra.firefox”, modify its value to Restart Firefox and now go to add-on site again; you can install the add-ons without any problem.

Remember to change the general.useragent.extra.firefox to the real version of Firefox after installing add-on so that you can be updated with new patches from Mozilla.You can try yourself with your add-on. Maybe you will find some problems when doing like I do. Then post a comment here we can discuss about them.

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