[ignoramous]

> I think TeeSpring has the right idea - they're checking that GA is loaded, if it is, then do stuff with it, if it's not, then don't.

I think they could go one step further and may be try...catch (sandbox) all access to third-party services that aren't critical.

User-agents, which browsers are, expectedly do put a lot of control in the hands of the end-users. Such breakages should be factored in and worked around (provided there are enough engineering resources to throw at the problem, of course).

[ryandrake]

Exactly. A browser's job as the user's agent is to do what the user wants it to do. It's not an ABI. If an end-user's browser is configured to do something you, as a developer, don't want or expect, and that breakage causes the loss of a sale, it's kind of on you: Either take a principled stand about "what browsers should be doing" and accept the lost sale, or try/catch around non-critical code to make your site more robust to the user's configuration choices.