Created attachment 403054 [details] Crash log There is a repeatable crash when opening a new window, either by clicking the application icon in the dock, or using the File -> New Window command. The start page is set to just showing Recent Items. The crash log (which has been "sent to Apple" multiple times, for what it's worth), is attached.
Thank you for the report! This is a known Safari issue in this build. Please verify with the upcoming build. In the meanwhile, it may be possible to work around with this Terminal command: defaults delete com.apple.SafariTechnologyPreview "NSWindow Frame BrowserWindowFrame"