Just ran into the problem that ZAP 2.8.0 doesn't list the localhost traffic in its history. After a bit, I found the solution here #5474
Since, as far as I can tell, this issue is not officially documented, it makes sense to update the FAQ for testing applications on localhost noting at least the solution for Firefox:
Go to: about:config
network.proxy.allow_hijacking_localhost = true
For the record, the help page was updated to mention that:
https://github.com/zaproxy/zap-core-help/blob/9b772751e493dec0a1418d216e3cf5d38d15d48f/addOns/help/src/main/javahelp/contents/start/proxies.html#L45
This thread has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.
Most helpful comment
Done in https://github.com/zaproxy/zaproxy/wiki/FAQlocalhost/_compare/d8fcae7a22ba6940a4a52f551d839437960edb70...d2e6e3b3e5eca80b0ff1be82e2adb8cf01b140da