[Affected versions]:

• Fx 72.0a1 (2019-10-31)
• Fx 71.0b6
• Fx 70.0.1

[Affected platforms]:

• Windows 10
• Windows 7

[Steps to reproduce]:

1. Access the about:preferences#search page
2. Click the “Add search bar in toolbar” option
3. Type something Inside the Search bar in order to trigger the dropdown opening
4. Press F 11
5. Observe the Search bar dropdown

[Expected result]:

• The Search bar dropdown adjusts its dimension accordingly, to match the Search bar width or it is just simple dismissed when user enters the fullscreen.

[Actual result]:

• The Search bar dropdown doesn’t properly adjust its dimension.

[Regression range]:

• Pushlog: https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=38d03bf4616e&tochange=283b5f38ce57
• Posible regressor: bug 1160014

[Additional notes]:

• The issue is reproducible also the other way around, when exit the fullscreen.
• The issue is fixed when reopening the search dropdown.
• On Ubuntu and macOS, the Search bar dropdown is instantly dismissed when entering fullscreen.

Too late for a fix in 70 but we could still take a patch for 71/72.

I think the suggested regressing bug looks most likely here. Moving across to Widget, since that seems most appropriate.

Jim, mind setting a priority?

The child window positions properly but maintains the width pulled from the normalized text box. Pretty corner case, but we'd love a fix!