STR: 1. Open Nightly with a clean profile 2. Navigate to http://7-zip.org/download.html 3. Download 7zip for your os Expected: Photon-themed download animation is triggered. Actual: Photon-themed download animation is not triggered. The photon-themed download animation works as expected when it is not your first time downloading. Video below: https://jwilliams-softvision.tinytake.com/sf/MTY5ODExNV81NjUxNjU3

:JW_SoftvisionQA can you confirm this is new behavior specific to the Photon theme? At this point in time, the icon has changed, but the animations for download starting, download finished have not changed, so I wouldn't expect any behavior change. You can create a build using MOZ_PHOTON_THEME= ./mach build to disable the flag and get the original theme back in a build from moz-central

I just verified when running MOZ_PHOTON_THEME= ./mach build this issue is still present. Just to verify, is the build being created even though I have these errors? $ MOZ_PHOTON_THEME= ./firefox -p Unable to read VR Path Registry from C:\Users\Justin\AppData\Local\openvr\openvrpaths.vrpath [GPU 9388] WARNING: pipe error: 109: file c:/builds/moz2_slave/m-cen-w64-ntly-000000000000000/build/src/ipc/chromium/src/chrome/common/ipc_channel_win.cc, line 346 ###!!! [Child][MessageChannel::SendAndWait] Error: Channel error: cannot send/recv Unable to read VR Path Registry from C:\Users\Justin\AppData\Local\openvr\openvrpaths.vrpath Firefox does still open.

MOZ_PHOTON_THEME is a build flag, so you'll only see an effect with the source checked out from mozilla-central, and building firefox locally with the flag set to false. You could also just try a nightly from before the new icon landed (and/or mozregression) to confirm this is new behaviour

Ok, I ran the steps to reproduce on the Nightly build from 06/08/2017 and the same issue happens there. I will close this as invalid since your code is not the issue here.