"Each version of Playwright needs specific versions of browser binaries to operate." [0]
They patch and compile browser binaries so they have the functionality Playwright needs.
Their build of Chromium is one release ahead of what's out but it looks like one could maintain a library of older Playwright browser binaries to test with. They probably have an older Firefox 91 binary that's feature-equivalent to the current Firefox ESR. Their WebKit builds won't ever be exactly the same as Apple Safari.
They patch and compile browser binaries so they have the functionality Playwright needs.
Their build of Chromium is one release ahead of what's out but it looks like one could maintain a library of older Playwright browser binaries to test with. They probably have an older Firefox 91 binary that's feature-equivalent to the current Firefox ESR. Their WebKit builds won't ever be exactly the same as Apple Safari.
[0] https://playwright.dev/docs/browsers