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Some earlier Firefox extensions, for one reason or another, may have not been updated to work on the latest Version of Firefox.

This is often very frustrating, as one may have found the extension very useful in the past.

Sometimes one can get round this problem oneself in the following manner:

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The key to resolving this question lies in the Program 7-zip.

Please download here

Learnt about 7-zip from a helpful post by Mafia_Penguin here

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The first stage is to download a copy of the .xpi of the Extension one wishes to modify.

There are different ways of doing this.

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1. The most elegant perhaps is to use Mr Tech Toolkit.

Go to AMO (Mozilla Add-ons) right click on Add to Firefox and you see the option Archive XPI

Once you have set up the Archive folder this is extremely fast and easy to do.
Thank you Mr Tech for this.

You may find on older extensions that the Mr Tech prompt does not appear on the AMO front page,
To remedy this click on See All Versions, the prompt will usually appear there.

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2. Another option is to right click on Add to Firefox and chose the option "save link as"

You will then have the following prompt:

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3 A third option is to use Internet Explorer. As it cannot install the .xpi file directly you are offered the option to save the file. In some situations you may find this method convenient. It is not the recommended method.

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OK so we now have the .xpi

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Modifying the .xpi
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Right click on the file and select the following option.
7-zip
Open archive

What 7-zip is doing is helpfully offering us the option to view the files without extracting them.

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What happens next is that 7-zip, again most helpfully, offers us the option to edit the install.rdf file while it is still in the archive.
Select the file (install.rdf) and then Right click on the file and select edit.
It is the install.rdf file that needs to be modified slightly.

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Once we go into Edit mode and look through the install.rdf file we will find the following information

You can see the line which includes the words maxversion.
This is saying that the file should not be intalled in a higher Version of Firefox than the one mentioned.

This is the information that we need to change.

Modify the text
Here the maxversion reads 2.0.0.*
This could be changed for example to: 3.0.*

Only the integers need changing.

And exit the Edit mode

At this point 7-zip most helpfully gives us the option to update the file in the archive.

Hit OK

And then close the Archive.

The .xpi file that you have left in front of you will have been modified

So you can now drag and drop it into your Add-ons and see if it works.

If you find there is a problem try re-editing the integer value.

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The explanation here may seem rather lengthy, but you will find when you have done this a few times that it can be a really fast process.

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So what 7-zip has helpfully allowed us to do is to edit the install.rdf file in situ, and allow us perhaps to continue using an extension that has fallen from grace.

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Thank you 7-zip

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Another approach to this whole question is to use Nightly Test Tools.
Please see this post by Mafia_Penguin

Using Nightly Tester Tools

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