Mozilla's Thunderbird email application is similar to the Mail application that is installed on every Mac computer. By installing the Lightning add-on, you can also view your calendar events, like the events stored in iCal, directly in the Thunderbird application. Once you install this add-on, you can also sync your iCal calendar events with the Thunderbird application, giving you the ability to use Thunderbird for all of your email and calendar needs.
Open a Web browser and navigate to mozilla.org. Click the "Our Projects" link, followed by the "Lightning and Sunbird" link. Click the "Mac OS X" link beneath the "Lightning" heading, followed by the "Download" link to download the Lightning add-on file.
Double-click the Thunderbird application icon to launch the application. Click the "Tools" menu and select the "Add-ons" option.
Click the "Settings" icon and select the "Install Add-On From File..." option. Locate the file you downloaded in Step 1, highlight it and click the "Open" button.
Click the "Restart Now" button in the Thunderbird application window to restart the application and install the add-on.
Double-click the "iCal" icon to launch the application. Click on the calendar you want to export to Thunderbird to highlight it. Click the "File" menu and move your cursor over the "Export..." menu option to view a drop-down list of options. Select the "Export..." option from the drop-down menu and click the "Export" button to export the calendar.
Click the "Calendar" icon in the Thunderbird application. Click the "Events and Tasks" menu and select the "Import..." option.
Locate the calendar file you exported in Step 5, highlight it and click the "Open" button to import the file into the Thunderbird application. Now you can view all of the events associated with the iCal calendar in the Thunderbird application.