Sometimes a problem with Firefox may be a result of malware installed on your computer, that you may not be aware of.

You can try these free programs to scan for malware, which work with your existing antivirus software:

• Microsoft Safety Scanner
• MalwareBytes' Anti-Malware
• TDSSKiller - AntiRootkit Utility
• Hitman Pro
• ESET Online Scanner

Microsoft Security Essentials is a good permanent antivirus for Windows 7/Vista/XP if you don't already have one.

Further information can be found in the Troubleshoot Firefox issues caused by malware article.

Did this fix your problems? Please report back to us!

The malware scans did not fix my problem. But I figured out how to get Mozilla launched without the error "class is registered." (This all came about when I deleted the address bar with conduit in it.) I have windows 8.1. All I do now is right click on the mozilla icon and select mozilla start page and it comes up. Don't know why I cant double click and get the start page like before, but hope to figure that out. Thanks for your response.

I suggest that you check the settings listed below, just to be sure.

Open a new window or tab. In the address bar, type about:config. If a warning screen comes up, press the Be Careful button. This is where Firefox finds information it needs to run. At the top of the screen is a search bar. Enter browser.newtab.url and press enter. browser.newtab.url tells Firefox what to show when a new tab is opened. If you want, right click and select Modify. You can change the setting to;

about:home (Firefox default home page),
about:newtab (shows the sites most visited),
about:blank (a blank page),
or you can enter any web page you want.

The same instructions are used for the new window setting, listed as browser.startup.homepage.

BTW, Conduit has been known to cause problems with some users.

You will have to decide to remove Conduit or not.

Close Firefox. Then Windows > Start > Control Panel > Programs > Uninstall..