How to fix error kmode-exception-not-handled in Mozilla Firefox

Solution Steps

1. 1 Restart Mozilla Firefox completely. Close it, open Task Manager (Ctrl+Shift+Esc), find any remaining Mozilla Firefox processes, right-click → End Task. Background processes from previous sessions are the most common cause of startup crashes.
2. 2 Update Mozilla Firefox to the latest version. Open the app, go to Help → Check for Updates (or download the latest installer from the official website). Updates fix known bugs and compatibility issues.
3. 3 Reset Mozilla Firefox settings. Navigate to %APPDATA%\MozillaFirefox and rename the settings folder to add '.old'. This forces Mozilla Firefox to create fresh settings — corrupted config files cause crashes.
4. 4 Run Mozilla Firefox as Administrator. Right-click the shortcut → Properties → Compatibility → check 'Run as Administrator'. Some features of Mozilla Firefox require elevated permissions.
5. 5 Check if Mozilla Firefox conflicts with your antivirus. Temporarily disable real-time protection and test. Add Mozilla Firefox installation folder to antivirus exclusions.
6. 6 Clear Mozilla Firefox cache. Navigate to %LOCALAPPDATA%\MozillaFirefox\Cache and delete all files. Corrupted cache data causes rendering and processing errors.
7. 7 Repair Mozilla Firefox installation. Windows Settings → Apps → Mozilla Firefox → Modify → Repair. This replaces damaged program files while preserving your data.
8. 8 If Mozilla Firefox still won't work: uninstall from Settings → Apps, restart, reinstall from official website. A clean install is the nuclear option but fixes almost everything.