A Firefox profile stores all of your important data, such as your bookmarks, history, cookies, and passwords. This article explains how to copy the files to a new profile, lists important files in the profile and describes what information is stored in these files.
If you are having a problem with Firefox then sometimes, rather than trying to find and fix the exact cause of the problem, it is easier just to make a new Firefox profile and copy your most important data over to it. The Refresh Firefox feature will do this for you automatically.
Before starting it is recommended that you make a complete backup of your existing Firefox profile in case something goes wrong. Please read the Back up and restore information in Firefox profiles article for instructions on how to do this.
For information on how to create a brand new Firefox profile, please read the Use the Profile Manager to create and remove Firefox profiles article, paying specific attention to the Creating a profile section.
Open your profile folder:
Click the menu button , click help and select Troubleshooting Information. The Troubleshooting Information tab will open.
Repeat steps 4-6 for each file you wish to transfer over to your new profile folder.
While copying your personal data from an old Firefox profile to a new Firefox profile, it is possible that you could copy over the file that is causing the problem you are trying to get rid of! The more files you copy over, the greater the chance of this happening. It is therefore recommended that:
This file contains all your Firefox bookmarks and lists of files you have downloaded and of websites you have previously visited. For more information see Create bookmarks to save your favorite webpages.
Your passwords are stored in two different files, both of which are required:
For more information see Password Manager - Remember, delete, change and import saved passwords in Firefox.
This file stores many of your Firefox permissions that are decided on a per-site basis. For example, it stores which sites are allowed to, or blocked from setting cookies, installing extensions, showing images, displaying popups, etc.
This file stores data about search engines available in Firefox.
This file stores any custom words you have added to Firefox's dictionary. If you have never added a custom word to the Firefox dictionary, then you will not have this file. For more information see How do I use the Firefox spell checker?.
This file remembers what you have searched for in the Firefox search bar and what information you have entered into forms on websites. For more information see Control whether Firefox automatically fills in forms.
Cookies are used by websites for a variety of reasons, some of which include keeping you logged in to a website you have previously logged in to, remembering any preferences a website has allowed you to set, authenticating you as a person who has visited a specific website before, etc.
This file stores all your security certificate settings and any SSL certificates you have imported into Firefox.
This file stores your preferences with respect to what Firefox does when it comes across known file types, such as whether you want to save a file or open it with a specific application. For more information see Change what Firefox does when you click on or download a file.
Based on information from Transferring data to a new profile - Firefox (mozillaZine KB)