This browser (unknown) is too old to run PlasmidPop. It works in Chrome or Edge 111, Firefox 114 and Safari 16.4 (iOS and iPadOS 16.4) or later, all from 2023. Nothing has been lost: files stay on your device.
Update Safari on its own, without upgrading macOS: open System Preferences > Software Update (on Ventura and later, System Settings > General > Software Update). Under “Other updates are available”, click More info…, tick only Safari, and click Install Now. Do not click Upgrade Now; that installs a new version of macOS.
Safari 16.4 needs macOS Big Sur (11) or later. On Catalina (10.15) or older, Safari stops at 15, so use a current Firefox or Chrome there instead.
On an iPhone or iPad, Safari updates only with the system: open Settings > General > Software Update and install iOS or iPadOS 16.4 or later. Other browsers on iOS use the same engine, so they do not help.
Update Chrome at chrome://settings/help.
Update Edge at edge://settings/help.
Update Firefox from Help > About Firefox.