From a2e92319830bda9649be194edc5ed711891a2331 Mon Sep 17 00:00:00 2001
From: gnattu <gnattu@users.noreply.github.com>
Date: Mon, 17 Nov 2025 11:14:19 -0500
Subject: [PATCH] Backport pull request #7335 from jellyfin-web/release-10.11.z

Blacklist Firefox native mkv playback

Original-merge: f2d2c5b26e16be0bec0d26674ad2b31ae6ebdab5

Merged-by: thornbill <thornbill@users.noreply.github.com>

Backported-by: thornbill <thornbill@users.noreply.github.com>
---
 src/scripts/browserDeviceProfile.js | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/src/scripts/browserDeviceProfile.js b/src/scripts/browserDeviceProfile.js
index 5fa1bc65d..e719c2a08 100644
--- a/src/scripts/browserDeviceProfile.js
+++ b/src/scripts/browserDeviceProfile.js
@@ -205,6 +205,13 @@ function testCanPlayMkv(videoTestElement) {
         return true;
     }
 
+    if (browser.firefox) {
+        // As of Firefox 145, its mkv support is buggy and causes playback issues because it would force preloading the
+        // whole mkv file before playback starts, which is extremely undesirable for streaming.
+        // See https://github.com/jellyfin/jellyfin/issues/15521
+        return false;
+    }
+
     if (videoTestElement.canPlayType('video/x-matroska').replace(/no/, '')
             || videoTestElement.canPlayType('video/mkv').replace(/no/, '')) {
         return true;