[matroska,webm @ 0xdf7650] Format matroska,webm detected only with low score of 1, misdetection possible!

i got the error when trying To concatenate multiple webm videos
after writing all the files i execute this:
```
await ffmpeg.writeFile(listFile, fileListContent);
await ffmpeg.exec([
"-f",
"concat",
"-safe",
"0",
"-i",
listFile,
"-c",
"copy",
"exam-unwrapped.mp4",
]);
```
i tried this on my machine and it was working, but when i try in firefox , it doesn't work and i get these in the log
`[matroska,webm @ 0xdf7650] Format matroska,webm detected only with low score of 1, misdetection possible! `
`Truncating packet of size 12131 to 685`
`[matroska,webm @ 0xdf7650] EBML header parsing failed`
`[concat @ 0xdee9f0] Impossible to open 'opening.webm'`
`file_list: Invalid data found when processing input`
`Aborted()`
note that the videos were in mp4 format then i converted them with this command:
`ffmpeg -i "input.mp4" -f webm -c:v libvpx-vp9 -c:a libopus "output.webm"`
thanks in advance