Are you reluctant to upgrade Firefox because your favorite add-on is incompatible? If you tried to install it anyway, you might be faced with the following notice:
Extension Incompatible Notice
Warning: Forcing to install extensions that are not updated to the current Firefox version may result in unexpected behavior. Continue at your own risk. Use Firefox Safe Mode to uninstall the add-on if anything goes wrong.
Method 1: Bypass Compatibility Check
Firefox checks if the add-on is compatible with the installed Firefox version during add-on installation. This check can be disabled through about:config.
Step 1: Type in about:config into the location bar. Click “I’m be careful, I promise!”. As it says, be careful here as this is like Firefox’s version of the Windows Registry.
Step 2: Type in ‘extensions.checkCompatibility’ (without quotes) into the filter box. If no results show, proceed to Step 3. If you find a boolean named ‘extensions.checkCompatibility’, toggle it so its ‘false’.
Step 3: Right click anywhere, and choose New, then Boolean.
Step 4: Type in ‘extensions.checkCompatibility’ and set the value as ‘false’.
Step 5: Restart Firefox and try installing your favorite extension again!
Step 6: If you are running Firefox 3.6, you must add an additional value: extensions.checkCompatibility.3.6 and set it to false.
Method 2: Nightly Tester Tools
The Nightly Tester Tools allows users to force install extensions regardless of their compatibility (assuming this add-on itself is compatible).
Method 3: Edit the Extension Compatbility
How does Firefox check if an extension is compatible? Inside the extension file lists the compatibility versions. Why don’t we edit that?
Step 1: Download the extension .xpi file by right clicking on the download button and clicking ‘Save Link As’ or by clicking the download button in another browser.
Step 2: Open the .xpi file with a Zip utility like 7-Zip (Windows). XPI files are zip files with a different extension.
Step 3: Extract and edit the file named ‘install.rdf’. It can be opened with any text editor. Do not use a word processor.
Edit the install.rdf file
Step 4: Search for a line with ‘<em:maxVersion>’.
Firefox Extension Version Compatability
Step 5: Edit the minVersion and maxVersion as needed. Wildcards are accepted. For example, for an add-on to install on all versions of Firefox 3.5, you would write ’3.5.*’ (without quotes). To force the QuickDrag to be compatible with Firefox 3.6 RC 1, I edited the file so that the targetApplication section looked like this (lines to edit are highlighted):
<em:targetApplication>
<Description>
<em:id>{ec8030f7-c20a-464f-9b0e-13a3a9e97384}</em:id>
<em:minVersion>2.0a1</em:minVersion>
<em:maxVersion>3.6.*</em:maxVersion>
</Description>
</em:targetApplication>
Step 6: Repackage the extension by compressing it into a zip file and renaming it into .xpi.
Step 7: Open the XPI file with Firefox by dragging it into the Add-ons window.
As I mentioned earlier, some add-ons might work perfectly, some might not work at all, some might have have strange behavior, and others may crash your browser. If something goes wrong, use Firefox Safe Mode to uninstall the extension. Force extensions at your own risk.
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