A command line tool (inspired by tape) can be used to test Firefox web extensions.
It starts Firefox in headless mode using Web Driver and install temporary test web extensions that are assumed to produce TAP output. You can use libdweb experimental test API which is API compatible with tape for writing tests.
You can run test web extension by running tape-ext from it's directory (directory containing manifest.json file) or you could pass glob to test multiple web-extensions.
tape-ext "test/*/manifest.json"
You can find usage examples at libdweb repository.