''locking - asked here - https://support.mozilla.org/en-US/questions/933572?s=&r=1&as=s'' I have a question related to editing preferences to alter firefox behaviors. In firefox, the permission for allowing and blocking website popups are stored in a SQLite database, namely permissions.sqlite, which is stored in users profile folder. I noticed that if I edit this preference in the database, I have to restart firefox in order to let the changes take effect. However, changing some other preferences can alter firefox's behavior right away. For instance, if I go to "Options->Tabs" and check "Always show the tab bar" option, the tab bar will show up immediately. It doesn't require a firefox restart. Some people told me that there are observers associated with certain preferences that can listen to preference changes and update firefox. Others told me that firefox will cache the preferences that are edited through the user interface and firefox can immediately aware of it. I am not sure which opinion is correct. My question is why editing certain preferences can change firefox's behavior right away while some other preferences requires a firefox restart in order to take effect?