My biggest gripe at Firefox 3 so far is the number of incompatible addons, which is by no means their fault. I did find a way around this. It is fairly simple, but carries a certain amount of risk with it as well. The extension developers may have made it up to 2.0 only for a reason.
Before doing this, however, try to find a website for the addon that is compatible. New alphas and betas are often, as in at least one I found (I can’t remember it at the moment, however).
For this guide, I’m going to use the Firebug extension. I wanted to use it, and couldn’t find a 3.0 alpha 8 compatible version.
Download the extension. Don’t install it, that is our problem. To do this, just right click and ‘Save link as.’ Save it into a temporary folder somewhere.
Now, change the extension on the file to .zip, as a .xpi is just a renamed zip. To accomplish this in Windows, go to folder options and turn on showing urls. I’m doing this from Ubuntu, and have them shown. Just rename it to a zip file. Now, extract that to a new folder called, for example, ‘firebug.’
In that folder will be a file called ‘install.rdf’.
Now, open the the file ‘install.rdf’ with your favorite text editor. I’m just using gedit, the default text editor for Ubuntu.
Find the line ‘2.0.0.*‘
Now, change this to 3.0a8, or whatever version you are using currently. It should now, for instance, look like this: ‘3.0a8‘.
Save the file and exit the editor. Now, select all of the files in the folder, and add them to a zip archive. You can do this with the built-in tool in Windows (Send to > Compressed Folder) or any archiver. The default archive manager in Ubuntu works perfectly for me. Name the zip anything you want.
As above, rename the file, but this time the other way, from .zip to .xpi.
Go into Firefox, and open addons. Click ‘Install,’ select the .xpi, and install. It should work perfectly.
[UPDATE:] To install this, you may have to open about:config and change ‘extensions.checkUpdateSecurity’ to ‘false’. This allows you to install extensions from non-secure sites. The check is a new feature in FF3.
Congratulations! You just installed an unauthorized addon!
Firebug works perfectly in Firefox 3 as far as I can tell, except it generates an error ‘_firebugTemp_ is not defined’ on every page. Not a big deal.
I’ve also used this method to install Scribefire, the extension I am writing this with. Check it out.
Well, that concludes the guide. Hope it helps someone!
If you are using linux, I scripted this in bash to make it a bit easier. See that article here.