- Remove the spacers next to the address bar. (I prefer having a huge address bar.)

- Install uBlock Origin, Bitwarden, and a few other extensions (GitHub Notifier, for example.) I don't use Firefox Sync right now, so I do this manually per install.

- Disable "Ctrl+Tab cycles through tabs in recently used order." I prefer the old Ctrl+Tab behavior where Ctrl+Tab moves right and Ctrl+Shift+Tab moves left.

- Set search to Duck Duck Go.

- Disable all Home content except Search.

- Disable browser, download, form and password history. Tweak content blocking settings a bit. (I generally 'block third party trackers' but I aspire to block all third party cookies if that ever becomes supported by most websites.)

Sometimes I also tweak other random things, like disabling the clipboard APIs entirely to avoid sites that attempt to add garbage to the end of copies. But realistically, these are the things that I usually keep the same. On portable devices I sometimes also enable permanent private mode, to keep even less sensitive data in storage.