Created attachment 682786 [details] stack+ 1. Create a profile with: user_pref("browser.ctrlTab.previews", true); 2. Launch Firefox 3. Ensure you have exactly one tab open 4. ⌘T, about:memory, Enter 5. ⌘T, about:memory, Enter 6. Ctrl+Tab Result: ###!!! ASSERTION: Invalid display item type!: 'type > TYPE_ZERO && type < TYPE_MAX', file nsDisplayItemTypes.h, line 69 This assertion is part of code added in bug 798964. When the assertion fails, type is nsDisplayItem::TYPE_ZERO.
Those STR do not work for me on Windows. Mac-only?
FrameLayerBuilder::BuildContainerLayerFor can pass 0 as the display item key when constructing a root layer. So if the root frame of the root document has a background image, we'll hit this assertion. I suspect that's what's happening here.
Created attachment 682964 [details] [diff] [review] fix