🐞The miniplayer should remain fully opaque (not transparent)

Description:
When scrolling the page and the miniplayer activates, it appears semi-transparent instead of solid. Because of this, it is difficult to clearly see the video and also hard to properly resize or move the miniplayer window. The transparency makes interaction imprecise and uncomfortable.

Steps to reproduce this:

Open any YouTube video

Scroll down the page so the miniplayer activates

Observe that the miniplayer becomes transparent

Try resizing or moving the miniplayer

Since when?:
Not sure exactly. Likely since a recent YouTube layout change or a recent extension update.

Browser:
Firefox, Vivaldi, chromium

Are any errors shown in the Browser-Console?:
No visible errors in the console.

The miniplayer should remain fully opaque (not transparent) and be easy to resize and move while scrolling the page.
I have Latest version from Firefox Add-ons store (exact version unknown).
Default settings (no custom configuration exported).
Desktop PC (Windows 11).

No file or test is named in the report. Start by reproducing the issue while scrolling a YouTube video in a supported browser, then trace the miniplayer's styling and activation path. Done means the miniplayer remains fully opaque and can be resized and moved precisely.