Replace default extension configs

[Vintic]

It is possible to modify default extension configs? If yes how could I do it?

I found something about it on uBlock page: but seems it is changed for all profiles, and some changes should be added into Windows registry.

Also I would like to modify not only uBlock add-on default configs.

[allo-]

This is not that easy since Firefox removed access to plain about:config keys for addons so they need to use other storages. There is a feature to add simple files, that is intended for things like this, see for example:

https://github.com/allo-/firefox-profilemaker/blob/23afadcf42e9c22c2a3cc68791bc6982d40d3854/settings/privacybadger.json#L4

The feature isn't very advanced and I think that's the only place where it is already used and it only works for the zip download.