Is NO_EM_RESTART actually recommeded, and why?

The documentation page for setting Firefox up to develop extensions, says this:

“Note that the extension manager automatically restarts the application at startup sometimes, which may mean you won’t have time to see the messages logged before the automatic restart happens. To see them, prevent the automatic restart by setting the environment NO_EM_RESTART to 1 before starting the application”.

What does this actually mean?

There are a few unfamiliar concepts to digest here. It says the extension manager automatically restarts the application at startup sometimes. But how can an app be restarted when it is restarted, since starting implies restarting. And if the app is starting anyway, what difference does it make if it is restarted when it’s starting. And what defines ‘sometimes’?

Moreover, is it actually recommended that NO_EM_RESTART is set to 1? The doc seems to be recommending it. But it doesn’t say what might be lost by doing this.

What does NO_EM_RESTART stand for? Is it documented anywhere?

Do you mean this documentation page?

The information on this page is outdated.
That’s why it says “Archive of obsolete content” and there’s a red/orange border around the page.

You can find up-to-date information at:

Thank you, yes, I did mean that page.

That’s the page that comes up most prominently in Google when you search a variety of related topics about setting up Firefox for developing extensions and, for example, trying to get the debugger to work.

I see now that its url has ‘archive’ in it. But I didn’t see, and can’t see anywhere on the page, anything that says the guide is out of date. I’ve been through it and made all the recommended changes to about:config.

Thank you very much for pointing me in the right direction.

The page you pointed out does not appear to say anything about needing to setup Firefox up to develop extensions. Do you happen to know if it is advised to change config settings to aid development? Ought I then undo the config settings recommended on the archived page?

There is still, however, no word on whether NO_EM_RESTART is recommended.

There are no required changes to develop extensions. You can use tooks like web-ext for a better experience (with fresh profiles). Or you can use the “developer edition” to get a browser that already has most of the debugging checkboxes checked. In other Firefox versions you will have to check some boxes the first time you want to debug something.

Okay, thank you freatechnik. So Developer Edition has check debugging checkboxes checked … that are necessary to run debugger?

All the same, that is another question.

Still, is NO_EM_RESTART actually recommended?

No, it is irrelevant these days and probably doesn’t do anything anymore in recent Firefox versions.

1 Like