(This may overlap with bug 1382232 - as both this and one of the comments there concern fonts, but the stacks are fairly distinct). The content process very frequently queries the OS to see if ClearType is supported -- it actually ends up doing this twice per "EndTransactionInternal" it looks like. The stacks look very similar, but are different: win32u!NtUserSystemParametersInfo USER32!RealSystemParametersInfoW+0x82 UxTheme!ClassicSystemParametersInfoW+0x29 UxTheme!_InternalSystemParametersInfo+0x29 UxTheme!ThemeSystemParametersInfoW+0xcb USER32!SystemParametersInfoW+0xa7 xul!mozilla::gfx::UpdateSystemTextQuality+0x13 xul!mozilla::gfx::Factory::UpdateSystemTextQuality+0x17 xul!gfxDWriteFont::UpdateClearTypeUsage+0xb xul!mozilla::layers::ClientLayerManager::EndTransactionInternal+0xa7 xul!mozilla::layers::ClientLayerManager::EndTransaction+0x5e xul!nsDisplayList::PaintRoot+0x9e8 xul!nsLayoutUtils::PaintFrame+0xc94 xul!mozilla::PresShell::Paint+0x61c xul!nsViewManager::ProcessPendingUpdatesPaint+0x138 xul!nsViewManager::ProcessPendingUpdatesForView+0x140 win32u!NtUserSystemParametersInfo USER32!RealSystemParametersInfoW+0x82 UxTheme!ClassicSystemParametersInfoW+0x29 UxTheme!_InternalSystemParametersInfo+0x29 UxTheme!ThemeSystemParametersInfoW+0xcb USER32!SystemParametersInfoW+0xa7 xul!UsingClearType+0x13 xul!gfxDWriteFont::UpdateClearTypeUsage+0x1e xul!mozilla::layers::ClientLayerManager::EndTransactionInternal+0xa7 xul!mozilla::layers::ClientLayerManager::EndTransaction+0x5e xul!nsDisplayList::PaintRoot+0x9e8 xul!nsLayoutUtils::PaintFrame+0xc94 xul!mozilla::PresShell::Paint+0x61c xul!nsViewManager::ProcessPendingUpdatesPaint+0x138 xul!nsViewManager::ProcessPendingUpdatesForView+0x140 xul!nsViewManager::ProcessPendingUpdates+0x4d Note that the first goes through |gfx::UpdateSystemTextQuality|, while the latter is |gfx::UpdateClearTypeUsage|. NtUserSystemParamersInfo is a win32k call, so we'd like to get it out of the content process.