Part One: With Firefox, back up the certificate as a .p12 file.
- In Firefox, click Edit > Preferences to display the Preferences
dialog.     
- On the Preferences dialog, click the Advanced button. 
- On the Advanced form, click the the View Certificates button to
display the Certificate Manager dialog. 
- On the Certificate Manager dialog, click the Your Certificates tab. 
- Expand the relevant certificate authority name and click the
relevant certificate to select it. 
- Click the Backup button to display a Save As dialog titled File Name
to Backup. 
- On the File Name to Backup dialog, in the Name text box, type the
name you want to give to the backup  copy of the file. 
- Select the folder in which you want to save the file. 
- Click the Save button to display the Choose a Certificate Backup
Password dialog. 
- Type your chosen password twice. Click the OK button.  
- An Alert dialog will appear, informing you that your certificates
and private keys were successfully  backed up. Click the OK button.  
- Close the other two open dialogs. 
Part 2: With Thunderbird, import the .p12 file to Thunderbirds certificate store.
- In Thunderbird, click Edit > Prefereces, to display the Thunderbird Preferences dialog. 
- Click the Advanced button on the top menu. 
- On the Advanced form, click the Certificates tab.  
- Click the View Certificates button to display the Certificate Manager dialog. 
- Click the Your Certificates tab. 
- Click the Import button to display the Certificates to Import dialog. 
- Find the .p12 file which you backed from Firefox, click it and click the Open button to display the Password Entry dialog. 
- Type the password you used to backup the file from Firefox and click the OK button. 
- An Alert dialog will appear, indicating that the operation was successfull. 
- Close the other two open dialogs. 
Part 3: In Thunderbird, edit the root certificate of your certificate authority to make it trusted for identifying websites, mail users and software makers.
- Display the Certificate Manager dialog as described in Part 2. 
- On the Certificate Manager dialog, click the Authorities tab. 
- In the list of root certificates, click on your certificate authority's certificate to select it. 
- Click the Edit Trust... button to display the Edit Trust Settings dialog. 
- Check the three checkboxes to make your certificate authority trusted for websites, email and software. 
- Click the OK button. 
- Close all open dialogs. 
Part 4: In LibreOffice Writer, verify that the certificate is available for digital signatures.
- Close all Writer windows which may have been running. 
- Open an existing Writer document (because you can only view the certificates from a file which is saved to 
disk). 
- Click File > Digital Signatures... to display the Digital Signatures dialog. 
- Click the Sign Document button to display the Select Certificate dialog. 
Your certificate will appear in the list of certificates.