If you are using Linux and the Gnome/Mate/Cinnamon desktop environments, Chrome stores passwords in the Gnome password manager (also known as Seahorse).
The following script will find these passwords, and export them to an XML password file that can be imported by the Firefox "Password Exporter" extension, so that, between them, you can transfer saved passwords from Chrome to Firefox.
Please see the top of the script for instructions, item 3. (The script also has other modes, for pure export/import of Seahorse passwords). You'll need to know how to install Python and related packages - this is not a point-and-click solution, sorry!