The most annoying thing about installing, un-installing and updating Firefox add-on is to restart the browser. Whenever you install/enable/disable/uninstall/update an add-on, you need to restart the Firefox to complete the changes. :( Google Chrome does not need to restart for installing/uninstalling /updating chrome extensions, and it is much easier to deal with the Chrome extensions.

Now, Mozilla developers are working on this problem, and the users will not require restarting the browser in future. Mozilla dev Dave Townsend describes this feature:
I’ve just implemented support for a special kind of extension that can install (and uninstall, and enable, disable, upgrade and anything else you can think of) without the user needing to restart Firefox. This is of course to allow add-ons developed on the Jetpack platform to install without restarts but the feature is going to be available to any extension author, there are just some restrictions to how these extensions work. [ more .. ]
Unfortunately, this implementation is not for all add-ons. Only those developed on Mozilla Jetpack platform will have this feature. According to Dave, this feature will be available to other add-ons only if they follow some restrictions.
This prototype is not final, and we hope that the restarting problem will be solved soon.
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