If you experience the serious firefox bug where the addon manager stops working and the addon window stays blank, then this extension might help you. Of course, it is not the final and neither the best solution to the problem but at least you can keep your browser working without reinstalling it or deleting your profile (which seems to be the only solution in most cases).
So if your addon window stays empty try the following:
1. Start firefox in safe mode and immediately close it.
2. Start firefox in normal mode and discover that the addon window will work again.
Note that it will only work for one time.
3. Install the Absolute Addon Bugfix Extension and restart the browser.
4. Now the only thing you will have to do is enable or disable the extension once per browser session.
Simply ignore the restart-prompt and continue browsing. The addon manager will continue to work.
Please note that there is no support for this extension. So if the described solution does not work for you, then just uninstall the extension and don't use it anymore. Consider directly contacting mozilla.org in this case.