I’m attempting to set a permanent new User Agent for Safari running on macOS Mojave (Developer Beta 10.14.0). However, it doesn’t work and changes to default each time. I ran the command below but it doesn’t seem to do anything. Is the behaviour possibly changed?

defaults write com.apple.Safari CustomUserAgent "\"Mozilla/5.0 (Macintosh; U; Intel Mac OS X; en) AppleWebKit/419 (KHTML, like Gecko) Safari/419.3\""
  • 1
    The currently available build is the first developer beta release of macOS Mojave 10.14. Updated the question to reflect the fact as beta release of OS are very likely to contain bugs and are liable to changes during short interval.
    – Nimesh Neema
    Jun 5, 2018 at 6:00
  • 4
    If it looks like a defect please report it to Apple via the usual way for Developer betas
    – nohillside
    Jun 5, 2018 at 6:30

1 Answer 1


If things stop working (or don't work as expected) after an upgrade to a beta version of Mojave the most likely cause is a bug in macOS (that's why it's called Beta after all). Best course of action is to report it to Apple using the usual feedback channels for beta releases, ideally in a way which makes it easy for Apple to reproduce the issue.

  • 5
    @Josh We are talking about the developer beta here, which Apple uses to gather feedback/bug reports. Posting bugs on AD doesn't improve the product, reporting them to Apple will.
    – nohillside
    Jun 6, 2018 at 14:13
  • @josh Please do so. I‘m not part of the Dev beta so I don‘t have the details
    – nohillside
    Jun 8, 2018 at 9:46

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