Mozilla Firefox requires you to enable permissions for the extension manually so you have to enable them to use PRMDB addon for Firefox.
Enabling permission is easy, just follow these simple steps.
1- Right click on the extension and select Manage Extension option in drop down menu.
2- On next page, select permissions tab and enable all the listed permission as you can see here:
3- Now reload the page of the website for which the extension is installed (ChatGPT or Bard), you will see the PRMDB's main interface.