Prefer WASM on firefox cause WebGPU is incredibly slow there.

docs/WorkBreakdown.md

@@ -247,6 +247,14 @@ Notes (M5):
       transcription start (file drop / live start) or via an explicit
       per-model Download button in `ModelPicker` — and never when the engine
       toggle is set to "server".
+- [x] Firefox performance: never run the WASM fallback single-threaded after
+      a failed accelerator attempt (worker posts `load-restart`, UI respawns
+      with explicit wasm — D-025); skip WebGPU when fp16 weights need the
+      absent `shader-f16` feature; hint that medium/large lag in live mode on
+      WASM. Field-verified: WASM now gets the full thread pool; ort-web's
+      WebGPU EP on Firefox completes but runs far slower than WASM, so
+      "auto" skips WebGPU on Firefox (D-026, explicit selection still
+      honored — retest on ort bumps).
 - [ ] Basic a11y pass (keyboard, focus, aria on progress/live transcript)
 - [ ] Production build + `bun start` deployment check; README for deployers