That will wipe everything, and when you restart Firefox, it’ll create a new Mozilla folder.
If you aren’t able to find the Application Data folder, it is probably because it is hidden. To make it visible, open up a folder and go to Tools->Folder Options->View.
Click on Show hidden files and folders and click OK. Then go back to step 1 and complete the process.
This method is only effective against casual privacy intrusions by nosey friends or parents. The data can still be retrieved through more sophisticated methods. More »