Firefox XPCOM error description: Firefox couldn’t open and the following error is displayed on screen: “Couldn’t load XPCOM”. The XPCOM error, may caused on a Windows based computer whenever a user tries to open Mozilla Firefox after a Windows Update or if the Firefox’s profile folder is corrupted. Firefox’s profile folder corruption may happen after a virus attack or after installing a third party extension on your Firefox browser.
This guide contains instructions to resolve the “Couldn’t load XPCOM” error on Mozilla Firefox browser.
How to FIX the “Couldn’t load XPCOM” error in FIREFOX (Windows – All Versions).
Important: Before applying the instructions bellow to resolve the XPCOM Firefox problem, make sure that your computer is virus/malware free by following the steps in guide: How To Scan Your Computer for Viruses and other Malicious Programs (Malware Removal Guide).
Method 1. Reinstall – Upgrade Firefox to the latest version.
1. From another Web browser (e.g. Internet Explorer, Chrome) download and Install the latest version of Firefox on your system. *
* Note: Do not uninstall Firefox, just run the Firefox Installer and follow the on-screen prompts to repair/upgrade the current Firefox application.
- Firefox Download.
Method 2. Start Firefox in Safe Mode and Disable Firefox’s Extensions (Add-ons).
1. Start Firefox in Safe Mode by following this procedure:
- Hold down the SHIFT key and then double click to open the Firefox application.
- Choose Start in Safe Mode
2. If Firefox starts without the XPCOM error message, then probably a Firefox extension (add-on) causes the “Couldn’t load XPCOM” error. At this case, disable one-by-one the installed Add-ons and then close and start Firefox normally, until you find out which plugin causes the problem.
To disable a Firefox plugin, from the main menu 
choose Add-ons
- At Extensions pane, Disable the installed Add-ons, (one every time) and then restart Firefox normally until you find out which extension causes the XPCOM problem.
- When you find out which Firefox extension causes the problem, then remove it completely (by starting Firefox in Safe mode).
– If after disabling all plugins, the XPCOM error persists then reset Firefox to Default Settings by applying the steps in next Method.
Method 3. Reset Firefox Settings to Default (Refresh Firefox).
1. Start Firefox in Safe Mode.
2. Choose Refresh Firefox.
3. Choose Refresh Firefox again. *
* Note: The refresh Firefox feature restores all browser settings to default, by creating a new user profile and by removing all Firefox’s Add-ons (extensions) and customization (preferences, plugins, added search engines). The Firefox Refresh doesn’t remove these items:
- Bookmarks
- Browsing history
- Passwords
- Open windows and tabs
- Cookies
- Web form auto-fill information
- Personal dictionary
Method 4. Uninstall and Re-install Firefox from your System.
Finally, if none of the above methods resolves the XPCOM error when starting Firefox, then:
1. Backup your Firefox Passwords, Bookmarks, Settings, etc.
2. Completely remove Firefox application and folders from your computer.
3. Install the latest Firefox version.
4. Restore your Firefox settings.
Method 5. Restore Your Computer To An Earlier Working State by using System Restore.
1. Try to restore your computer to a previous working state in order to resolve the XPCOM error in Firefox.
- How to Restore Windows 10, 8 or 8.1 to a previous working state
- How to Restore Windows 7 or Vista to a previous working state.
That’s all folks! Did it work for you?
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