First, make the hidden files visible. To do this you open your file manager, click on “View”, and then select “Show Hidden Files.” Navigate to your home folder, and look for “.mozilla”. Your bookmarks, passwords, extensions, and account settings are all stored there. Copy this folder to a USB memory stick. Firefox is now backed up.
To restore your backed up files on a new install, you will need to again make hidden files visible, and navigate to the “.mozilla” folder. Delete everything in the folder, but don’t delete the folder itself. Now just copy and paste the contents of the backed up version of “.mozilla”. Then start Firefox, and all your bookmarks, passwords, extensions, and account settings will be restored.
Personally I take the period of the front so I know it’s on the USB memory stick. Otherwise I might not know it’s on there if I am viewing it without hidden files showing.