URL: https://www.instagram.com/reels/

Browser / Version: Firefox Mobile 138.0
Operating System: Android 15
Tested Another Browser: Yes Edge

Problem type: Design is broken
Description: Items are misaligned
Steps to Reproduce:
Summary
Instagram Reels (instagram.com/reels) do not display correctly in Firefox for Android — the current video splits between the previous and next Reel, requiring manual screen holding to view properly.

URL
https://www.instagram.com/reels

Browser
Firefox for Android
Firefox 138.0

Platform
Android
Device: POCO M6 Pro 5G
OS: Android 15

Problem Type
Video or media doesn't display or play correctly

Steps to Reproduce

1. Open Firefox for Android.
   2.Navigate to https://instagram.com/reels and log in if necessary.
   3.Scroll through the Reels.
   4.Observe how the video area behaves when switching between Reels.

Expected Behavior
Each Reel should be shown one at a time in full screen, similar to the Instagram app or Chrome browser. The video should auto-align without requiring user intervention.

Actual Behavior
The video display splits: the top half shows the previous Reel, and the bottom half shows the next Reel.

To view the current Reel properly, I must manually hold the screen.
Once I lift my finger, the split-screen reappears.
This makes it difficult or impossible to watch Reels properly on Firefox for Android.

The issue does not occur in Chrome or the Instagram mobile app.
It seems to be a rendering issue related to viewport handling or CSS scroll snapping on Firefox Android.

Happens consistently with all Reels content.

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