I have an Ubuntu Linux server where I download various on-line videos for later playback.
The playback is through an Apache webserver page where the available videos are listed and where the user can click on a link to bring up a video player in which the content is shown.

This has been working for several years, but recently I discovered that there is a difference between playing back on FireFox or Chrome, where the audio/video sync is off when using Firefox but spot on for Chrome using the same playback URL.

At first I thought that it was a server side problem and tried to figure out from where the mis-sync was coming, it is about a whole second or more.
But then I discovered that when using Chrome there was no sync problem and the same if I played the same file from the file system using for example the VLC player.

So what can cause FireFox to behave differently in this case?
I have tested both Chrome and FireFox from my own PC as well as from my ASUS tablet and the same is happening: Chrome=OK, FireFox=big mis-sync (about a second or so).

If I use "view source" I get this for the video player part concerning the video file:

Code:
</head>
<body>
<div>
<video id="myVid" controls autoplay>
<source src="2025-01-19_19_NEWS.mp4" type="video/mp4" />
</video>
<div>
What can cause the browsers to execute so differently?
And is there something I can do to correct this on the source side?