The URL background color for Photon on Linux is now gray rather than white. It's because "-moz-field" is misspelled as "mos-field" in the theme CSS: https://dxr.mozilla.org/mozilla-central/source/browser/themes/linux/browser.css#271

Name Firefox Version 55.0a1 Build ID 20170518030213 Update Channel nightly User Agent Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:55.0) Gecko/20100101 Firefox/55.0 OS Windows_NT 6.1 I know that this Bug is A. about Linux and B. A DUPLICATE of Bug 1365275 However, I saw a very similar 'grey URL bar', for the first time on 2017-05-17, that looked like https://bug1365789.bmoattachments.org/attachment.cgi?id=8868782 I was hoping that your fix would be in today's Nightly (Build ID 20170518030213) but I still see the 'grey URL bar'. STR: Use Build ID 20170518030213 on a new Profile Background is still grey (both URL Bar and Search Bar). Seen on First Run. See Screenshot "Windows-Nightly-x64-2017-05-18-First-Run-on-New-Profile.png" DJ-Leith

Opened a new Bug 1366276 "Grey background to URL and Search Bar, Nightly 55.0a1 (2017-05-17), on Windows 7 using "Windows Classic" theme" To track this issue. DJ-Leith