Affected versions

• 74.0
• 75.0b4
• 76.0a1 (2020-03-16)

Affected platforms

• Windows 10
• Ubuntu 18.04

Steps to reproduce

1. Make sure you are logged into Office365
2. Go to https://office.live.com/start/Word.aspx?omkt=en-US&auth=1&nf=1
3. Open any available file
4. Reduce the browser’s width until “Tell me what you want to do” string is replaced by “Search”
5. Hover the Search field

Expected result

• The input field respects its range

Actual result

• The Search input field overlaps the Editing button

Regression range

• Reproducible way back to 54.0a1, on older builds I can’t access the site.

Additional notes

• Not reproducible on Chrome
• Refreshing the page has no effect
• The issue is fixed when typing something inside the field

Ksenia, would you mind taking a look here?

The input with id TellMe-SearchBox has a width: 100%; and overflows its flex parent (adding min-width: 0 to the input styles fixes this).
This is a duplicate of https://bugzilla.mozilla.org/show_bug.cgi?id=1585485