Firefox has the ability to save bookmarks and all settings for that matter to a local folder upon closing the browser, you could then use an open source and hop

Firefox has the ability to save bookmarks and all settings for that matter to a local folder upon closing the browser, you could then use an open source and hopefully encrypted sync tool to replicate those backups. Might be a bit clunky at first but if it catches on I'm sure one of the open source sync tools will come up with some sort of integration.