firefox: Speech Dispatcher library missing

When starting firefox (I think since 116) it shows this message:

I tried adding speech-dispatcher to firefox inputs as well as installing it to the profile. Yet this message still shows up.

diff --git a/nongnu/packages/mozilla.scm b/nongnu/packages/mozilla.scm
index 967388d..5e8c320 100644
--- a/nongnu/packages/mozilla.scm
+++ b/nongnu/packages/mozilla.scm
@@ -65,6 +65,7 @@
   #:use-module (gnu packages rust)
   #:use-module (gnu packages rust-apps)
   #:use-module (gnu packages sqlite)
+  #:use-module (gnu packages speech)
   #:use-module (gnu packages video)
   #:use-module (nongnu packages wasm)
   #:use-module (gnu packages xdisorg)
@@ -533,6 +534,9 @@ MOZ_ENABLE_WAYLAND=1 exec ~a $@\n"
             (replace 'set-build-id
               (lambda _
                 (setenv "MOZ_BUILD_DATE" #$%firefox-build-id)))))))
+    (inputs
+     (modify-inputs (package-inputs firefox-esr)
+       (append speech-dispatcher)))
     (native-inputs
      (modify-inputs (package-native-inputs firefox-esr)
        (replace "rust" rust-firefox)

But the speech-dispatcher seems to work as following command results in a "hallo" from my loud speakers

$ guix shell speech-dispatcher -- spd-say hallo