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This add-on works you need to modify the install.rdf file.
We'll have to edit the addon, make it compatible with your new version of Firefox and then save it.
What a XPI file?
An XPI file is a zipped file containing the files needed to install and use the extension.
In an XPI file, there is a file called install.rdf that includes several parameters including one that tells Firefox which versions it is compatible. So just change these settings.
Get the file. Xpi
If you already own Xpi file, skip this step.
If it is an extension hosted at https: / / addons.mozilla.org, here's how:
With a browser other than Firefox
(IE, Opera, Chrome, Safari ...)
Go to Mozilla Addons page of the extension.
Left click "Add to Firefox". If download save dialog comes up then save the file to your computer.
Right click> on the button "Add to Firefox" and go to properties.
In the "Properties", copy the link where the advanced button (for example : https: / / addons.mozilla.org / en-US / firefox / downloads / latest / xxxx / xxxxxxxx.xpi? src = addondetail )
Paste in the address bar the link (https: / / addons.mozilla.org / en-US / firefox / downloads / latest / xxxx / xxxxxx.xpi? src = addondetail)
A download window opens, save the file to your computer.
It's good, you have the file. XPI!
Edit the file. Xpi
Now extract the Xpi file with the any software like IZArk or 7zip.
You need to change the extension of the file. Rename your file's extension from xxxxxxxx.xpi to xxxxxxxx.zip
Extract the files from your extension, the zip file.
Find the file install.rdf and open it with a text editor such as Notepad
Look for the line
<em:minVersion> 1.0 </ em: minVersion>
<em:maxVersion> 20.* </ em: maxVersion>
MaxVersion change or minVersion suit your needs: maxVersion to put 20 to be quiet until version 20 of Firefox.
Save the file
Re-archive the files to . Zip
Rename the file from xxxxxxxx.zip to xxxxxxxx.xpi
Install file. Xpi in Firefox
Open Firefox on any webpage
Do a drag and drop into Firefox window
A window asks if you want to install the extension!