vivaldi download is unbelieve slow.
I would download the vivaldi for window 64bit from the download page.
The download speed is 24KB/s and make firefox download timeout and suspend.
Sure I had check my network speed is fine when download anything else.
Can not reproduce it. I get 5.7 MByte/s.
Speed here are normal, you could try with a download manager, but it shouldn't be necessary at all.