Affected platforms:
Windows 10 pro
Arm64
Affected versions:
nightly 85.0a1 (2020-12-10) (64-bit)
beta 84.0

Steps to reproduce:

1. open a random youtube video
2. click pip button
3. once pip window is on bottom right corner, adjust screen through the right border, top or bottom, to the minimum size (black borders are already triggered in small window version)
4. close pip using Close the Picture-in-Picture button (left button next to pause, not the X)
5. click pip again (without refreshing), to trigger pip window
6. pip window is still displayed small, same size as when it was closed in step 4
7. resize window to be bigger

Expected results:
Pip window should be corrected displayed.

Actual results:
Black borders are displayed, it looks rectangular, not square.

Notes: this won't happen if adjusting with left borders. In Firefox release it's not reproducible either, when clicking close pip button, and clicking pip button to open window once again, the size of window is reset to original value.

Regression range: Will provide one ASAP.

Suggested Severity: I will suggest an S2 , as user can refresh youtube to fix this problem.

Resubmitting video due to quality.

Just a heads up, I meant to clone the product and component and not duplicate the bug https://bugzilla.mozilla.org/show_bug.cgi?id=1551058, my apologies! I didn't mean to have all of you cc'ed to this bug.
Best regards,
Clara