Avast Web Shield block file uploading

Avast Free Antivirus / Premium Security
1

Windows 7 (64-bits)
Avast Free Antivirus 17.3.2291 (build 17.3.3443.0)
Firefox 52.0.2 (32-bits)
URL: http://www.mpb.gov.tw/theme/traffic/Trf_report.asp

This is a web site to update video of traffic violation (Sorry it’s Chinese Traditional).
After I input all the fields and click “upload” icon, Firefox doesn’t transmit any data to the web site and display “connection timeout” a moment later.
And I can’t find any log about the reason why the Web Shield block the connection.
This can be solved if I disable the Web Shield.
Thanks a lot for your help.

2

Does it work with other browsers ?

3

Yes, it works fine with IE even the Web Shield is ON.