There are two options:

1) First you can export the data from Chrome and then import it to Firefox but this is hard.

2) If you only have only a few passwords saved in Chrome you may open the Chrome Browser, then tap the thre little dots and then passwords here you can see all of the passwords that are stored in Chrome. Now you can open Firefox and tap on your Profile or the little head in the top left bar where you can also seethe Downloads and the history, there you can tap on passwords or lockwise. Now a new window with Firefox Lockwise should open, there you can add passwords. If you just login to a service Firefox will also ask you if you want to store the login.

As a footnote to the above:

Firefox Sync does not share Firefox data with your Google account, or vice versa, even if you set up your Firefox Account using a Gmail address. They are completely separate systems.