The bookmarks and history are both stored in the same places.sqlite database.

You backup specific files with Firefox closed to the current profile folder.

• https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile

• bookmarks and history: places.sqlite
• favicons: favicons.sqlite
• bookmark backups: compressed .jsonlz4 JSON backups in the bookmarkbackups folder
• cookies.sqlite for the Cookies
• formhistory.sqlite for saved autocomplete Form Data
• logins.json (passwords) and key4.db (58+) or key3.db (57 and older) (decryption key) for Passwords saved in the Password Manager
  if you only have key3.db then make sure to remove an existing key4.db
• cert9.db (58+) or cert8.db (57 and older) for (intermediate) certificates stored in the Certificate Manager
  if you only have cert8.db then make sure to remove an existing cert9.db
• persdict.dat for words you added to the spelling checker dictionary
• permissions.sqlite for Permissions and possibly content-prefs.sqlite for other website specific data (Site Preferences)
• sessionstore.jsonlz4 for open tabs and pinned tabs (see also the sessionstore-backups folder)

You can use the button on the "Help -> Troubleshooting Information" (about:support) page to go to the current Firefox profile folder or use the about:profiles page.

• Help -> Troubleshooting Information -> Profile Folder/Directory:
  Windows: Open Folder; Linux: Open Directory; Mac: Show in Finder
• https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data

See also:

• https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles

What about extensions and theme?

You can backup the extensions folder, but backing up extension's data is complicated as this data is stored in local storage (indexedDB; storage folder in the profile folder) and the UUID to link this to the extension is stored in prefs.js (visible on about:config under extensions.webextensions.uuids). You can see this extension info in about:debugging under "This Firefox".