Feature and motivation

Firefox Addon endpoint supports either path or addon parameter, with addon being a base64 encoded string of a compressed file, which can be either an xpi or a zip file.

Directories are needed to support the temporary parameter. Rather than implementing a file detector and trying to upload the directory to a remote machine, directories should be zipped and base 64 encoded and sent with the addon parameter.

Supporting temporary parameter is #10084
It was fixed in every language, except .NET has outstanding PR — #10093
So, it works if the user zips the directory and passes it in, but it would be nice for Selenium to do this for the user.

A great example of this by @nickgaya in JS is here:
#10216

Usage example

String id = ((HasExtensions) augmentedDriver).installExtension(Paths.get("path/to/addon/directory/"), true);