Steps to reproduce:
Please install the attached extension in Chrome and click "Allow in Incognito" in the extension details. A new tab page should have a green background. An Incognito window a red one. In Orion its always green, because the object property "tab.incognito" is always false. Btw a switch like "Allow in Incognito" in extension settings should exists, and extensions should not run in incognito windows by default.
As used in attached extension "tab.incognito" should be "true" in an incognito window.
Orion and macOS:
Version 0.99.107.16-beta (WebKit 613.1.8)