[BUG] firefox screenshots differ between headless and headed

[dgozman]

Here is an example from the tests:

playwright/tests/screenshot.spec.ts

Line 23 in 5f1188d

browserTest.skip(({ browserName, headless }) => browserName === 'firefox' && !headless, 'Firefox headed produces a different image.');

From my local testing on MacOS, headed screenshots are correct when using deviceScaleFactor: 2.5, and headless screenshots are wrong.

[aslushnikov]

Merging into #12683

[amrsa1]

When this fix could be released