Is there a way to disable the "Welcome to Firefox" popup when creating a new profile?

[FriedGenera]

The popup seems to interfere with the application of user.js on startup, I don't remember having to launch Firefox the first time before having to put user.js into the root directory then relaunching it a second time for it to apply on a new profile, I could just open the root before launching the profile the first time and put user.js into it. Is there a way to avoid this behavior?

Edit:It also deletes the user.js if I put it in before the first launch

[yokoffing]

Is there a way to disable the "Welcome to Firefox" popup when creating a new profile?

Try adding user_pref("browser.startup.homepage_override.mstone", "ignore"); to your user.js.

I don't remember having to launch Firefox the first time before having to put user.js into the root directory then relaunching it a second time for it to apply on a new profile, I could just open the root before launching the profile the first time and put user.js into it. Is there a way to avoid this behavior?

I do vaguely recall an experience where opening Firefox for the first time a certain way would ignore or remove the user.js on first launch. It's been awhile.

Another way to go about this is to launch Firefox under the default profile, and then go to about:profiles to create a new profile, and put the user.js in there. Once you restart, go back to about:profiles and make sure you click Set as default profile for the new profile.