Many Firefox malfunctions or errors are caused by add-ons or changes in settings; by resetting the browser (the function is officially called "reset"), you should be able to fix most of them. You can restore some of the lost information with a little extra work, or you can manually change your preferred settings.
Steps
Method 1 of 3: Reset Firefox
Step 1. Go to the Firefox troubleshooting page
Open a new browser tab and type about: support in the address bar. You should see a page titled "Troubleshooting Information".
- You can access the same page by clicking on the ≡ icon (top right) →? (bottom right) → Troubleshooting.
- If both methods don't work, click on this link and then on Solution 1.
Step 2. Click on the Firefox reset button
Search Reset Firefox… in the upper right corner of the screen.
Step 3. Confirm the action
Click the Reset Firefox button once again in the dialog box and when done select Finish in the second window. This procedure closes and reopens the browser making the following changes:
- All added extensions, themes and search engines are deleted.
- All settings are restored to default, including key layouts and preferences.
- Your download history is cleared, so make sure you know which folder your downloaded files are in.
Step 4. Erase all old data
Mozilla recommends deleting the folder on the desktop named "Old Firefox Data" that appears when the browser is reset. If you want to recover some of your settings, first read the instructions in this section.
Method 2 of 3: Reset Firefox When It Won't Open
Step 1. Open Firefox in Safe Mode
This way, you can reset it even if it crashes when you open it normally:
- If you have a Windows computer: Hold down the ⇧ Shift key while opening the browser. If that doesn't work, search your computer for "Mozilla Firefox Safe Mode".
- If you have a Mac computer: Hold down the ⌥ Option key while opening Firefox.
- For Linux devices: type the command / path / to / firefox / firefox -safe-mode from the Terminal.
Step 2. Press and hold the same button while choosing a profile
After opening the browser, a list of profiles appears; select one by keeping the key activated while clicking with the mouse. This step is only necessary if you have more than one profile on your computer.
Step 3. Select "Restore Forefox"
Before the browser window appears, you can see a dialog with two buttons. Select that Refresh Firefox to reset settings and delete add-ons; please note that this is a permanent change.
Alternatively, select Start in Safe Mode to see if these steps resolve the issue for the current session. If so, manually disable some add-ons and restart your browser normally; if you don't get results, restart the program again in safe mode and reset Firefox
Method 3 of 3: Restore Data after Reset
Step 1. Check which data is missing
You can use this method to reset search engines, some website-specific settings, and download preferences, which are generally not a source of errors. If this data has been lost, you can recover it with the instructions described here.
If you want to reset add-ons or settings, change them manually and don't follow this method; by recovering them from the back-up, you run the risk of generating the same errors
Step 2. Open the troubleshooting page
Type about: support in the address bar or follow this path by clicking on the icon ≡ →? → Troubleshooting.
Step 3. Open the profile folder
You can find the relative button at the top of the screen, on the left side of the page. The words that identify this key change according to the operating system on your computer and the version of Firefox:
- Windows: Show folder;
- Mac: Show in Finder;
- Linux: Open Directory;
- Firefox 13 or earlier (for any operating system): Open the content folder.
Step 4. Find the old data
The system should have saved the pre-restore ones in a folder on the desktop. If you can't find it, search your computer by typing the words "Old Firefox Data".
If you are using a Windows computer, you may need to show hidden files
Step 5. Close your browser
You should always close it before changing profile settings.
Step 6. Copy the files to your current profile
Open the "Old Firefox Data" folder and choose the files you want to transfer; by continuing to read, you will find instructions to identify them. Right-click on the file name and select Copy. Open the new profile folder, right-click on an empty space in the folder and select Paste.
- If you are using a Mac computer, hold down the Ctrl key and click on the file name with the right mouse button.
- If prompted, choose whether to replace or overwrite existing files.
Step 7. Choose the files to transfer
It is best to copy as little as possible, as they may be responsible for the errors. Here are some suggestions of the files you should copy:
- search.json: related to added search engines;
- permissions.sqlite: contains the preferences of the various websites that are allowed to collect cookies, open dialog boxes and so on;
- mimeTypes.rdf: contains preferences for managing downloaded files (with which program a certain type of file opens).
- Firefox tries to automatically restore the files listed below. You don't have to recover them yourself, unless an error occurs during the procedure.
- places.sqlite - bookmarks and history;
- key3.db And logins.json: saved passwords;
- formhistory.sqlite - information for automatic filling of online forms.
