***DISCLAIMER***
Notice I said many times you can do this. This will NOT work on all extensions. However, if you attempt to bump the version and it doesn't work, you just remove the extension wihtout hurting your Firefox installation.
Step 1
Find an incompatible extension to install on your current version of Firefox. For our example, let's try installing the Google Pagerank extension, version 0.9.6 on Firefox 2 RC1. It's only certified with Firefox 1.5b2, so if you attempt to install, it will give you an error message. You must download the .xpi file. Many developers (such as the Pagerank developer) give you a link to download the .xpi. If they don't, just right-click the install link, and choose 'Save Link As...' and pick a place to save it to.
Step 2
Next, if you don't already have it, go download and install a copy of 7Zip. It is a free, open source archive manager alternatvie to WinZip. Just follow the defaults of the installation.
Step 3
After installing 7Zip, find the .xpi file from Step 1 and right click the file. Choose 7Zip > Open archive
It will open the .xpi file in 7Zip. It will look very much like viewing a .zip file in WinZip:
Step 4
You will need to find the file names install.rdf. In our example, it's right there in the root of the archive. Select the file and hit F4 This will open the file in Notepad or your text editor of choice:
You will notice the .rdf file is just a basic XML document. Find the tag named em:maxVersion and simply change 1.5+ (or whatever is there on the extension you're editing) to 2.*.
So this:
Becomes this:
That's all the editing. Next, just save and close the file. 7Zip will detect that an internal file was changed and ask you if you'd like to update it in the archive:
Click 'OK' and then close 7Zip
Step 5
All you have to do now is open Firefox and drag the .xpi file anywhere onto the browser window. After doing so, you'll be presented with the common extension installation box:
And that's it! Now the Pagerank extension works for Firefox 2 RC1!
