How to Automate Firefox Configuration/Customization?

Group Policy: https://github.com/mozilla/policy-templates/releases
If it's a local stand alone PC, find the policy, and use the registry instead.

I would like to set Firefox as my default browser.

In the white windows 10 search box, search for, 'Default Apps".  Find Web Browser, click and select Firefox.

When I open Firefox, I would like to display three tabs;

Start firefox, open up the three tabs you want. Then go to settings and search for, "home".  Once there, where you see, "Homepage and new windows" select the, "Use Current Pages" button.

I would like to stop having the pop up box in the upper right corner telling me of a new firefox version.

I don't know if this will work as you expect. In the settings, search for, "update". Perhaps unchecking, "Use a background service to install updates. Also change the radio button from Automatic to "check for updates but let you choose to install them"  I think that is as close as you will get.

I needed to be more specific with my question.  Here's the better wording:
I would like to automate the following Firefox tasks in windows 10. Is there a way of scripting this?  Or a macro?

Why? I have to do this to 100 pcs.

I would like to set Firefox as my default browser.
When I open Firefox, I would like to display three tabs; each one showing a particular site.
I would like to stop having the pop up box in the upper right corner telling me of a new firefox version.

I would like the above to be accomplished by a bat file or a script.  Currently I’m doing all of the above INDIVIDUALLY    THIS IS TOO TIme-Consuming 

As said, the group policy takes care of this all.
Default browser, is a Windows Policy, the rest are done in the Mozilla policies.

Hi Kim:
Where is Mozilla policies located?
I'm in Local Group policy editor now.
I could not find the settings in Group  policy?

I can't find a search facility in Group policy.