supervisor: Upload backup fails with "unsupported file format" under Firefox for Windows

Describe the issue you are experiencing

I am not able to restore a backup made by HomeAssistant on a new installation.

Clicking “Alternatively you can restore from a previous backup” and selecting a previous tar backup always results in a pop-up stating “Unsupported file format - Please choose a Home Assistant backup file (.tar)”.

Trying to upload a backup under Settings / Systems / Backups leads to the same error.

What is the used version of the Supervisor?

2022.05.1

What type of installation are you running?

Home Assistant OS

Which operating system are you running on?

Home Assistant Operating System

What is the version of your installed operating system?

5.10.108

What version of Home Assistant Core is installed?

2022.5.4

Steps to reproduce the issue

1. Using HAOS on a Raspberry Pi 3B, I created a backup as follows : Went to Settings / System / Backups Selected “create backup” Waited about a half hour (!) for the backup to be created
2. Once complete, I clicked the vertical … menu, and “download backup” to get the file onto my Windows PC
3. On my PC, fired up the Virtualbox VM running HAOS (Linux)
4. Logged into http://:8123 in my Firefox browser
5. Clicked “Alternatively you can restore from a previous backup”
6. Selected the tar backup file I downloaded in step 2
7. I got a pop-up stating “Unsupported file format - Please choose a Home Assistant backup file (.tar)”.
8. I then created a dummy account and went to Settings / System / Backups
9. Using the vertical … context menu, I clicked “Upload backup” and selected the tar file from step 2
10. I got the same error as in step 7

Anything in the Supervisor logs that might be useful for us?

N/A

Additional information

I installed the SSH add-on and uploaded the tar backup to HAOS using WinSCP, and was then able to restore it successfully. This proves that the backup file itself wasn’t the issue. It looks like there may be a problem with the backup file upload process.

The browsing I’m using is Firefox 100.0 on Windows x64, FYI.

In thread https://community.home-assistant.io/t/moving-haos-to-a-different-hardware-platform/421608/6, other users mentioned that there was a bug in the past related to backup file size. I’m not sure if this is the same problem I’m experiencing here. The tar backup file is 715 MB in size.