Force-press the left edge of the screen, then swipe to the right. It can take a little bit of practice to get a hang of it. I find kinda rolling my thumb works well to trigger it. Swiping all the way across goes to the last app, just partway opens up the app switcher.
What about killing a tab in chrome? In android, I could hit back and it would kill that tab and take me to the previous one, which works beautifully for Reddit. With iOS it's like five clicks to get back to the previous tab.
