Well first start if you do a simple internet search you could find this help pretty fast. There are some basic thing one can do to get the info faster in this help as well. https://support.mozilla.org/en-US/kb/how-do-i-set-sync-my-computer

Warning: Some data cannot be shared between different versions of the Firefox programs. You can sync bookmarks, history, and passwords. https://support.mozilla.org/en-US/kb/how-do-i-set-sync-my-computer Sync your bookmarks, history, passwords, add-ons and open tabs with another copy of Firefox. Learn how to set up Sync. https://support.mozilla.org/en-US/kb/how-do-i-choose-what-types-information-sync-firefox We'll show you how to choose which types of information (bookmarks, history, add-ons, and passwords) to share across all your devices through Firefox Sync. https://support.mozilla.org/en-US/kb/firefox-sync-troubleshooting-and-tips https://support.mozilla.org/en-US/kb/sync-firefox-bookmarks-and-browsing-history-iOS Sync your passwords, history, tabs and other browsing information across your iOS, Android and desktop computers with Firefox Accounts.