Comment 1 for bug 1771380

It's not just the omnibox that's unresponsive for some time at startup. It appears that anything that involves keyboard input is delayed, e.g. opening the task manager with Shift+ESC, or opening a new tab with Ctrl+T (however opening a new tab by clicking on the button to the right of the first tab is instantaneous, but then pressing a key to start typing in the omnibox lags by the same delay).