Can no longer browse without Charles running
It is likely that your browser’s proxy settings have been changed to use Charles and then, for some reason, not changed back.
First try starting and quiting Charles normally to see if that corrects the problem. Because if Charles is stopped abnormally (such as a crash) it doesn’t have an opportunity to reset your proxy settings. It should notice that when it is restarted.
If that doesn’t work you’ll need to fix your proxy settings manually. How you do this depends on what application is misconfigured:
Windows / Internet Explorer
First quit Charles. Then go to the Internet Options in your Control Panel. Go to the Connections tab. Click on the LAN Settings. You’ll see a Proxy panel. Uncheck the Use a Proxy checkbox. Click OK until you’ve closed the Internet Options.
Mac OS X
Go to your System Preferences. Open the Network preferences. Choose the appropriate Network Port (you may need to reconfigure more than one if you have more than one) and click Configure. Go to the Proxies tab. Look in the list of proxy servers, you will see that Web Proxy and Secure Web Proxy are active. Uncheck those or reconfigure them as required for your network. Click Apply Now and then close the Network preferences.
Firefox
First quit Charles. Then go to the Firefox Preferences window, General tab, click Connection Settings. Then choose “Direct Connection to the Internet” or enter whatever proxy settings are required for your network. Click OK and then close the Preferences window.