1. Open FireFox
2. Click on
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3. Once the Options Windows opens, click on 'Find in Options' and type in 'Certificates'
4. Click on 'Select one automatically'
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5. Click on 'View Certificates'
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6. Once the Certificate Manager window has opened, ensure that that the Authorities tab is selected and then click on Import
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7. Find and select the certificate file to import, click on Open
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      1. note the certificate name may be different, but the extension will always be a .cer.
8. Ensure that both tick boxes are checked and click on OK.
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9. Click on OK in the Certificates Manager window
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10. Close Firefox and relaunch.