To import bookmarks and other data from another browser installed on your Android device:
- Sign into your account on a desktop copy of that browser.
- Once signed in, install a desktop copy of Firefox onto that computer.
- With Firefox installed, follow this guide to Import data from another browser
- Now that the data is in Firefox, you can then follow this guide to either set up a Mozilla account or add the desktop copy of Firefox to your existing Mozilla account.
On your Android device, when signed into the same account in Firefox, your bookmarks, passwords and other data will be synced across.