Wavebox includes a compatibility layer that allows extensions that utilize the Firefox contextual identities api to interact with Wavebox cookie containers in the same way.
The full ContextualIdentities API documentation is available on the Firefox website.
The API is still experimental and needs to be enabled on a per-extension basis. To do this, open wavebox://extensions in a new tab, locate the extension and open the detail view. From here contextual identities support can be enabled.
The API is at present read-only. This means the following calls will fail...
contextualIdentities.createcontextualIdentities.updatecontextualIdentities.remove
The way in which Wavebox generates cookie store ids differs to Firefox. Extensions that hard code ids may need updating