As of Firefox 1.0PR, Firefox no longer by default will allow third party sites (sites not hosted on update.mozilla.org) to install extensions. When you attempt to install an extension you should see a warning message like the following appear on top of your browser window:

Click on the "Options..." button to bring up the following window:

Click on Allow to allow ffxi.xenoveritas.org (this website) to install extensions. After this, you can click on the Install button again to actually install the extension.

I've also run into one other bug with the way extensions work. If you do not allow the page to completely load then clicking on the Install button will not work. This appears to be because Firefox and Mozilla consider any action taken while the page is "loading", regardless of what caused the action, to be an "automated action" and blocks it as a security risk. The idea is to prevent sites from automatically attempting to install extensions onto your computer.

Mozilla 1.8 implements a whitelist of sites that are allowed to install extensions. Right now, there doesn't appear to be any UI to allow you to add sites to that whitelist, so you can't install the extension at all.

You can add the site to the whitelist by going to "about:config" in your browser. Filter on "xpinstall" and look for a key marked "xpinstall.whitelist.add". Edit this value (by double-clicking on it) and enter "ffxi.xenoveritas.org" as the value.

You should then be allowed to install the extension. (Note that there's no UI to remove this later, so if you ever want to forbid me to install extensions, you'll need to edit the "hostperm.1" file in your Mozilla profile directory.)

If you have any other issues with Mozilla, please send me an e-mail.

This may effect Mozilla, I'm not sure. I've run into one other bug with the way extensions work. If you do not allow the page to completely load then clicking on the Install button will not work. This appears to be because Firefox and Mozilla consider any taken while the page is "loading", regardless of what caused the action, to be an "automated action" and blocks it as a security risk. The idea is to prevent sites from automatically attempting to install extensions onto your computer.