image upload just uploads ~~junk~~ random data

Summary

Summarize the bug encountered concisely.

Steps to reproduce:

How one can reproduce the issue - this is very important.

1. Step 1 goto: https://gitlab.torproject.org/-/profile
2. Step 2 press choose file
3. select jpg image file
4. you see the image correctly, press upload
5. profile picture is scrambled
6. gitlab.torproject.org asks you to enable and allow canvas in TB, why?

What is the current bug behavior?

What actually happens.

See my profile picture. This not only the result on gitlab.torproject but Mozilla profiles for example too

What is the expected behavior?

What you want to see instead

Upload works or ask user to enable canvas?

Environment

Which operating system are you using? For example: Debian GNU/Linux 10.1, Windows 10, Ubuntu Xenial, FreeBSD 12.2, etc.

10.0.18 (based on Mozilla Firefox 78.11.0esr) (64-Bit)

Which installation method did you use? Distribution package (apt, pkg, homebrew), from source tarball, from Git, etc.

tpo http://scpalcwstkydpa3y7dbpkjs2dtr7zvtvdbyj3dqwkucfrwyixcl5ptqd.onion/

Relevant logs and/or screenshots

See my profile picture for screenshots. Zoom inside and out