1656800 - Positioning issues in FF DevEdition

Status: RESOLVED DUPLICATE of bug 1655398

(Core :: CSS Parsing and Computation, defect)

Description

[Albert Scheiner [:alberts]]

Note: The following issues do not occur in stable (79) nor in Nightly (81).

I ran into two issues with the current DevEdition which now point to be an bug in Firefox.
FF 80.0b2 (64-bit); macOS 10.15

So far I did:

• test with add-ons disabled
• refreshed my profile (about:support) and reinstalled everything
• deleted FF DevEdition and reinstalled it
• created a new profile with the newly installed DevEdition

#1 Header starts jittering when scrolling down

1. Go to https://yahooeng.tumblr.com/post/96098168666/important-announcement-regarding-yui
2. slowly scroll down

Expected

I smaller Yahoo logo only appears once the white content area reaches the top of the viewport

Actually

When scrolling from the top down the hero including some elements start to jitter. This starts ~300px from the top to ~600px from the top.

#2 JS positioned dropdown and datepicker misaligned

1. Go to https://legalvision.com.au/documents/letter-of-termination-of-employment-redundancy/?form=true
2. Scroll down to "What is the date of this letter?" and click into the field

Expected

A calendar appears top or bottom aligned to the field.

Actually

The calendar is positioned somewhere at the top of the page (changes a bit with the scroll offset of the input field).

The same is true for the select boxes in the form. The dropdowns also appear way on top.

Comment 1

[Emilio Cobos Álvarez (:emilio)]

I think this is bug 1655398 (should be fixed in b3)

Comment 2

[Albert Scheiner [:alberts]]

Yeah, that seems likely. Will test again once b3 the is out and then close it as dup if it works. Ni? myself