There are upcoming new features and underlying changes to Firefox which will cause the AE Creations extensions to stop working. If you are using the stable release of Firefox (version 42 at the time of this writing), then this won't impact you. However, if you are using Firefox Developer Edition (formerly known as Aurora) or Firefox Beta, then you need to be aware of a few things.
In a nutshell, this new feature, sometimes referred to as Electrolysis or e10s, runs the web page content and the browser chrome code in separate processes.
Clippings, Panic Button, Send Tab URLs and Delicious Post will all break. If you want to run these extensions in Firefox Beta or Firefox Developer Edition, turn off multi-process tabs. You can do this in the browser preferences page. These extensions will be updated over the next few months to support Electrolysis, so stay tuned.
Clippings users on Thunderbird should not be impacted by this change.
Some users have reported that Clippings has stopped working on Firefox 44 alpha (the current Firefox Developer Edition version) because of the ES6 compatibility change that was introduced in this Firefox release. To work around this issue, install the latest beta release of Clippings 5.0.