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Performance timeOrigin can be significantly in the past

Making moves

While building out some RUM observability code, I noticed that the `performance.timeOrigin` could be significantly in the past for some users. I don't know why or how this happens but I am wondering if it has anything to do with the browser preloading the page, or some other interaction with cache like bfcache. I have seen this issue in Firefox, Chrome, and Edge which leads me to believe my understanding of `performance.timeOrigin` is not right.

The assumption that I am currently working from is that `performance.timeOrigin` is the precise moment the page began loading (which the definition for is up for debate) while `` is the milliseconds since that time. It's the latter part of that assumption that I really seem to have a problem with.

The data:


  // Everything below is data from in-browser
  "": 1712869191634, // Browser time at time of execution
  "global.timeOrigin": 1712866335518, // Value of `performance.timeOrigin`
  "global.navigationStart": 1712869187273, // Value of `performance.timing.navigationStart`
  "localTimeDiff": -2851493, // `global.timeOrigin - global.navigationStart`
  "timeSincePageOrigin": 4361, // Value of ``
  "originTime": 1712866335518, // Value of `window.performance.timeOrigin`
  "userAgentName": "Firefox",
  "userAgentOS": "Mac",
  "userAgentVersion": "124.0"


From the data, it appears the browser context was create ~47 minutes before navigation started. What am I misunderstanding here?