Safari practically never does that shit, which is one of the reasons I prefer it on platforms where it's available. IDK why modern Firefox is so damn eager to interrupt me. Just open a window with my last session or my default tab and shut up. I don't care if you just updated. I don't care if you're weirdly-enthusiastic about introducing me to a feature that hasn't been novel in a browser in at least a couple decades (color themes—LOL, that was just embarrassing). I certainly don't want an actual advertisement. And for god's sake, no, I still don't care about Pocket, and I never will.
For less-technical users, this stuff isn't just annoying, it can disrupt their entire browsing session. "Wait... where's my email? Is it gone? Is this the right program?" Firefox (and other teams that do crap like this, in their products) should knock it off. It is not OK.