Hi, sorry but you will need to go to Gmail/Google to request get your passwords reset. That is the whole point of having a master password is for your protection as per any other password protect site on the web which you decided to avail yourself of this feature.

You will need to reset your password in Firefox but all data will be lost. https://support.mozilla.org/en-US/kb/reset-your-master-password-if-you-forgot-it

G'luck

Please let us know if this solved your issue or if need further assistance.

Did you save your Google account credentials in Firefox's password manager, or is Firefox able to get into those accounts simply because it is preserving a cookie set the last time you visited?

Password Manager

You can check your password here:

• Windows: "3-bar" menu button (or Tools menu) > Options
• Mac: "3-bar" menu button (or Firefox menu) > Preferences
• Linux: "3-bar" menu button (or Edit menu) > Preferences
• Any system: type or paste about:preferences into the address bar and press Enter/Return to load it

In the left column, click "Privacy & Security".

Then on the right side, click the "Saved Logins" button. Then click the "Show Passwords" button.