Found in

• 107.0a1 (20221016093143)

Affected versions

• 107.0a1 (20221016093143)
• 106.0
• 105.0.3

Tested platforms

• Affected platforms: Windows 10x64
• Unaffected platforms: Ubuntu 20.04, macOS 10.15

Steps to reproduce

1. Open the about:preferences page and scroll down to the Fonts area.
2. Click on the Advanced button and observe the content from the Fonts window.

Expected result

• The window is opened as expected and no visual issues occur.

Actual result

• The content of the Fonts window shakes upside down when opened.

Regression range

• Last good revision: 5d4ec1262b2e579217133d276309e6ccdce1c28a
  First bad revision: b2bdddc979f368917b07162504961bc5690fff8a
  Pushlog:
  https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=5d4ec1262b2e579217133d276309e6ccdce1c28a&tochange=b2bdddc979f368917b07162504961bc5690fff8a
  Potential regressor: bug 1784488.

Additional notes

• Attached a screen recording of the issue.
• Note that a slight content move can be observed before bug 1784488 as well when the window is opened but now the content is shaking.
• Note that sometimes the issue may be intermittent.

:dao, since you are the author of the regressor, bug 1784488, could you take a look?

For more information, please visit auto_nag documentation.

fontbuilder.js builds these lists asynchronously; there was an attempt to set the height of the menulists such that there's no visual change once they fill up (bug 1704113) but this is tricky because it depends on the size of the text that ends up selected in the menulist when it finishes building. I don't know that there's a straightforward way around this, and as this is an S4 I'm not sure it's worth spending a lot of time on this either.