On macOS there is a native affordance for this by using force click. It's kind of annoying that Firefox chose to not support this and instead made it click-and-hold only.
I agree with the other comments that say it's not discoverable. I've been using MacOS for 10 years and I didn't even know that "Force Click" is a thing. This comment caused me to look it up and then try it.
I disagree that it's "everywhere". I just tried it in Spotlight Search (Command + Space). I can never remember how to see where a thing is located there and I hoped a force click might show me. Hint: pressing command will do it but it takes 250ms to 500ms to show up and somehow I never wait that long.
Not only does Spotlight Search not show me where it is, force clicking doesn't show me a preview, or seem to do anything else.
In Finder force click edits the name of the item you're clicking. So, this doesn't seem to be terribly universal.
I suppose I'll slowly figure out how this works now that I'm aware of it.
Back when Chrome was still trying to gain traction, they came out supporting native Keychain Access for password management. Firefox, which had a 4 year head start, never implemented it.
- Inigo Montoya
This is no affordance. There's nothing the design of either browser that suggests you can obtain a link preview by those actions, you just have to be told what action to take beforehand.