From 5c444198ea80ba75bffbfbaf7599adcf7a603f5e Mon Sep 17 00:00:00 2001
From: gnattu <gnattuoc@me.com>
Date: Sun, 16 Nov 2025 01:42:01 +0800
Subject: [PATCH] Blacklist Firefox native mkv playback

---
 src/scripts/browserDeviceProfile.js | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/src/scripts/browserDeviceProfile.js b/src/scripts/browserDeviceProfile.js
index 5fa1bc65d5..e719c2a081 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;