In Firefox, there are several different areas to add a trusted site (referred to as “Exceptions“), depending on what functionalities you want to allow the site to do or prevent the site from doing.
From the Firefox menu, go to Tools > Options.
Under Content, you can keep the security option to Block pop-up windows, but then Exceptions… to add URLs for the sites where you want to allow pop-ups.
In the Exceptions… dialog box, enter the web site URL in the Address of website: field; then click Allow.
You may also select and remove any of the exception sites in the list.
Under Privacy, you can choose to Never accept Cookies from sites, but then enter some Exceptions to allow them on specific sites.
You can also click Show Cookies… to examine the cookies stored from various websites, and Remove them if you wish.
Under Security, if you have the “Warn me when sites try to install add-ons” box checked, you can allow certain sites to override this warning by clicking Exceptions.
Under Advanced, click the Network tab. There is a checkbox labeled Tell me when a website asks to store data for offline use. Here you can add Exceptions that would override this rule.
— Back to Browser Information