Updated April 28, 2025
When it comes to computer repair, the most common problem I find is browser corruption. Malicious browser extensions are the most common way a browser can get corrupted. So here's how to clean up and reset Mozilla Firefox.
I've shown how to clean up and reset Google Chrome and Microsoft Edge, so this article shouldn't be a surprise. What might surprise you is that all three browsers are installed on my personal computer, and Firefox is my default browser. Each has pros and cons, but since Firefox is a product of the Mozilla Foundation (a non-profit organization), I prefer supporting them.
I've always considered Mozilla Firefox a cross between Internet Explorer and Google Chrome, having the best elements. A case in point is how you can access the options in Firefox. You can either use the Menu button in the upper right-hand corner (the button with three (3) horizontal bars, similar to the three dots in Chrome) or enable the Menu Bar on top of the browser window (similar to Internet Explorer).
To get the Menu Bar, right-click the blank area above the Address Bar and select Menu Bar. Some options can only be accessed using the Menu Bar, but I'll discuss that later in this article.
Let's start with the necessary options. If you're using the Menu Button, select Settings; if you're using the Menu Bar, select the Tools pull-down menu and then Settings. This will bring up the Firefox preferences. On the left-hand side is a list with several selections; General, Home, Search, Privacy & Security, Sync, Firefox Labs, More from Mozilla, Extensions & Themes, and Firefox Support.
The first panel on the left-side menu is General and is where you will find the most basic settings: Startup, Import Browser data, Tabs, and Browser Layout. Also, under the General section, you will also find Language and Appearance, Files and Applications, Firefox Updates, Performance, Browsing, and Network Settings.
These settings are mainly personal preferences that configure how Firefox looks and works. Under Files and Applications you will find the Downloads section. This is one setting I always change, as I prefer to be prompted as to where I want to save a download, as I don't always want them just saved into my default downloads folder.
Right below Downloads is Applications. Here you can choose what happens when you select different actions, like when you click a mailto: link. There is nothing really out of the ordinary here. I would review them to make sure everything looked good. If you think something is questionable, just change the action. You can always change it back if it doesn't work how you want it to. Below Files and Applications is the Firefox Updates section; make sure that Automatically install updates (recommended) is selected.
The second panel is Home and includes Homepage and new windows, New tabs, and the Firefox Home Content. If Firefox has been modified by a malicious piece of malware/adware, you'll want to check the Homepage and new windows and New tabs settings to ensure they are not opening up malicious web pages when Firefox starts. If any of the settings have been changed, you can reset Firefox back to the default settings by clicking on the pull-down menu and selecting Firefox Home (Default).
The next panel on the left-side menu is Search. This is where you configured how Search works in Firefox.
You can select what search engine Firefox uses from a preset collection of the most popular search engines. You also can have a separate search bar or use the address bar for navigation and search. If you decide to use the separate search bar, you can change the search engine it uses on the fly by clicking on the magnifying glass on the Search box's left side.
The next panel is Privacy and Security. In this section, you have to go through each subcategory and make sure the settings will work for you. Right out of the box, these settings are pretty perfect, although there are a couple I prefer to configure for my taste.
Under Browser Privacy, you can select how Firefox handles website tracking. The default setting (Standard) works fine, but you can restrict what a website can do if you want to. But remember that with stricter security policies, you may break or disable the functionally of some sites.
In the Cookies and Site Data section, you can manage the website data that Firefox stores. Here, you can clean out the cookies and cached data from websites. You can automatically have Firefox clean out this data when you close it, but that setting is in the History section (see below).
The Passwords section is, as the name implies, where you configure Firefox to save usernames and passwords or not. If you plan on using the Sync feature, you will want to have Firefox save this data.
The next section is the Autofill area. If you want Firefox to automatically fill out website forms with your data (name, phone, email address, etc.), make sure the Save and fill address and Save and fill payment methods checkboxes are selected. You can edit any saved data here, too.
In the History section is where you can have Firefox clear data when you close it. If you pull down the selections under Firefox will: and select Use custom settings for history, you get a few more options. I recommend that you check Clear history when Firefox closes box and then click on the Settings button.
You can choose what items you want Firefox to delete when it is closed in the window that appears. I deselect everything but Cache. But this is strictly a personal preference.
Next is Permissions, and there are two (2) items you want to make sure are selected: Block pop-up windows and Warn you when websites try to install add-ons. Firefox Data Collection and Use comes next. It is your preference if you want to enable any of these options.
Under the Security section, make sure that Block dangerous and deceptive content, Block dangerous downloads, and Warn you about unwanted and uncommon software are selected. The Certificates section is, again, personal preference, but the default settings are just right.
The next panel on the left side menu is Sync. This is a cool feature if you have Firefox installed on multiple devices. I use this feature with a couple of computers and a smartphone. I love how it will sync saved passwords across all of my devices. Enough said.
The next panel is Firefox Labs. Here you can reset Firefox back to default and try some experimental features.
The More from Mozilla panel has links to some of their different products.
Now that we've checked/reset and changed the preferences let's look at the add-ons section. There are three (3) ways to get to it:
- On the Settings page, click on the Extensions & Themes link at the bottom of the left-hand column.
- Click on the Menu Button (3 horizontal bars) in the upper-right hand corner and select Add-ons and Themes.
- On the Menu Bar, left-click on Tools and select Add-ons and Themes from the drop-down menu.
Once you have the Add-ons page up, you will find four (4) selections on the left side menu; Recommendations, Extensions, Themes, and Plugins.
The first selection is Recommendations, which, as the name implies, are extensions and themes that Firefox recommends. Pretty simple.
The second selection on the left side is Extensions. This is where you look for malicious apps that like to run inside Firefox. Go through the list here, and if you find one that you don't remember installing, just click the Enable / Disable slider on the right-hand side.
You will be prompted to restart Firefox to disable it altogether. Remember that even if you disable an extension, you can always enable it at a later date. Or if you find you don't need it at all, you can always delete it. But remember that if you delete an extension and then realize you did want it, you will have to reinstall it.
The next selection on the left side menu is Themes, and this is where you change the look of Firefox. If you don't like the default theme, you can always download a new tone using the Find more themes button at the bottom of the right-hand column.
The fourth selection down the left side menu is Plugins.
Plugins add support for different types of Internet content, like videos and encrypted media.
Now, if after going through the previous steps and Firefox is still not working the way it did when you installed it, there are two (2) things you can do. You can either reset it or uninstall/reinstall it. Usually, a reset will fix about 90% of Firefox problems, but sometimes, only an uninstall/reinstall will work. I always try a reset first.
To reset Firefox, you will need to have access to the Menu Bar. To get the Menu Bar to appear, just right-click the blank area above the Address bar and select Menu Bar from the context menu. Once you have the Menu Bar, left-click on Help and then More Troubleshooting Information.
When the Troubleshooting Information page appears, click on the Refresh Firefox button on the page's right side. You will be prompted on how you're about to reset Firefox back to its default settings. Click on Refresh Firefox, and Firefox will be reset back to its original default settings. It also creates a folder on your desktop called Old Firefox Data, just in case you need to restore anything, like your bookmarks.
Now, if that doesn't get Firefox back to normal, then the last resort is to uninstall/reinstall. This may take a little time to perform, but if you really want Firefox back to pristine condition, this is what it might take. There are two (2) ways to uninstall programs in Windows; the Settings app or the Control Panel.
Uninstall a program using the Settings app
- Click on the Start
menu, then Settings (the gear icon), then Apps. then Installed Apps.
- Scroll down the list of apps in the right-hand column until you find Mozilla Firefox.
- Highlight Mozilla Firefox and click on the three (3) horizontal dots to the right and select Uninstall.
Uninstall a program using the Control Panel
- In the search box next to the Start button type Control Panel and click on it from the results.
- Select Uninstall a program (if viewing by category) or Programs and Features (if viewing by icons).
- Highlight Mozilla Firefox and click on the Uninstall button.
Once Mozilla Firefox is uninstalled, restart your computer. When your computer is rebooted, and you are logged back in, you will need to remove any traces of Firefox before reinstalling it. There are three (3) places that you will need to look for any leftover files, two (2) inside your user profile and one (1) inside of the Program Files directory. The files inside your user profile are hidden by default, but you can get there quickly by bringing up a Run dialog box (Windows Logo key + R) and typing or copy/paste the following lines:
%userprofile%/AppData/Local/Mozilla %userprofile%/AppData/Roaming/Mozilla
This will open the File Explorer to the locations of your Firefox user profile settings. If there is a folder named Firefox, go ahead and delete it. Next, you will have to navigate to the location of the Program Files directory and check under the folder named Mozilla Firefox. Its location is usually C:\Program Files\Mozilla Firefox, but it may be different if your Windows version is 32-bit or if you installed Firefox on a different drive. Once you get there, go ahead and delete it. Now you can download and reinstall Mozilla Firefox.