Enabling extension for private windows after installing it with geckodriver

[hheexx]

I am installing web extension into firefox over selenium with /moz/addon/install endpoint. How can I enable it for private windows? (newly added setting in firefox addon manager).

You may need to add new parameter to endpoint or is there other way?

### Tasks
- [ ] https://bugzilla.mozilla.org/show_bug.cgi?id=1561841

[whimboo]

Please see https://bugzilla.mozilla.org/show_bug.cgi?id=1561841 which we might make it part of the WebDriver session capabilities.

[hheexx]

Thanks. I solved it by bundling custom profile with preinstalled extension.