It’s not so much that they’re blocked, they just don’t work because ios Firefox is actually safari. It’s the same with all browsers on iphones, they’re all safari.

Apple only allows different browser engines in the European Union, but even there they came up with enough requirements that they aren’t allowed in practice:

https://developer.apple.com/support/alternative-browser-engines/

From a skeptical translation point of view, I want to know if the word heart means the same thing today as it did then.

I’m sure that part is mostly accurate, but I think it’s talking about other people’s hearts, rather than one’s own.

In context, it’s trying to make a point about how one should trust god above men, because there’s no way for one to know how another person truly feels (but in theory god can).

You’d have to ask a theologian for an actual answer.