tools/translate-spike/spike.mjs loads a Bergamot build under plain Node, builds an en-de model from Remote Settings files and translates text and inline HTML. Firefox's v3 build (bergamot v0.6.0) and npm @browsermt/bergamot-translator 0.4.9 both load current models at about 540 words/s on the built-in fallback matrix multiply, with no browser globals needed once Module.wasmBinary is supplied. Firefox's build is chosen: it ships with the models and links its own gemm imports. apps/desktop/features/translate/DESIGN.md records the plan: engine in a utility process, model catalogue and cache, page session, content script, lazy feature tile and declared-language detection.