https://bugs.winehq.org/show_bug.cgi?id=38960
--- Comment #53 from Robert Walker bob.mt.wya@gmail.com --- (In reply to Olivier F. R. Dierick from comment #52)
For you information. Steam December 12, 2016 update includes, among other things: "Updated web control to CEF v55.0.2883. This version requires Windows 7 or macOS 10.9 and above, users on older OS versions will continue running the existing version."
Yup as expected that breaks, all web browser content, in Wineprefixes set to Windows 7. Even when running the Steam client with the -no-cef-sandbox commandline switch.
Hopefully they'll stick to this policy of not pushing this CEF update - e.g. on users with a Wineprefix Windows version of Windows XP.