Prerequisite: Make sure you have a "group MMS" thread. If you don't have one, please create one: 1. Open the messages app. 2. Press the "new message" button. 3. Press the top right button, choose "add subject". 4. Type something in the subject. 5. Enter at least 2 recipients; 6. Press send. You'll need a SIM to reproduce, but you can enable flight mode to create the group thread without sending the MMS, we don't need that the MMS is actually sent. STR: 1. Make sure the SMS app is closed. 2. Lock your phone. 3. Send a SMS message the device. 4. Click on the notification to enter the SMS app. 5. Press "back" to enter the Inbox view. => Observe the group MMS does not have any contact displayed anymore. Only the word "MMS" is displayed.

The root cause is that window.innerWidth is 0 when the phone is locked. I don't know if that's expected.

Hey Tim, would you know why window.innerWidth is 0 when the phone is locked? Or do you know who can know? Is it expected?

Stepping through Gecko w/ gdb should give you the answer, in the mean time, this is the related code path (I think...): https://dxr.mozilla.org/mozilla-central/source/dom/base/nsGlobalWindow.cpp#4727 nsGlobalWindow::GetInnerWidth(JSContext* aCx, JS::MutableHandle<JS::Value> aValue, ErrorResult& aError) https://dxr.mozilla.org/mozilla-central/source/dom/base/nsGlobalWindow.cpp#4711 int32_t nsGlobalWindow::GetInnerWidthOuter(ErrorResult& aError) https://dxr.mozilla.org/mozilla-central/source/dom/base/nsGlobalWindow.cpp#4726 nsresult nsGlobalWindow::GetInnerSize(CSSIntSize& aSize) Somewhere here returns 0 and that's what you get. I am throwing this to Core::Layout because I don't observe the same behavior on desktop.

I created a testcase here: https://everlong.org/mozilla/test-innerwidth.html I checked on Desktop and Firefox/Android and I don't see this behavior. So let's close this bug as it's likely Firefox OS only.