Portage gathers your bookmarks, history, cookies, tabs, sessions and reading list into one portable JSON bundle, and writes your extension list to a separate checklist file. Because it's just JSON, you can import it into any browser running Portage — Chrome ↔ Firefox, or the same browser on a new machine or profile. Nothing leaves your machine, and the data is wiped from memory the moment you export.
Keep encryption on (above) so the .portage.json is unreadable on disk. Portage holds your data only in this page's memory and wipes it after export — it's never written to extension storage. Either way, delete the file once you've imported.
…or click to choose a bundle exported from any browser — Chrome, Firefox, or the same one. Encrypted bundles will ask for your passphrase.