To avoid this permanently in Firefox 23+
Please follow the below mentioned steps.
1. Open Firefox web browser and type about:config in address bar.2. The following screen will appear.
3. In the above screen click the button I’ll be careful, I promise!.
4. The following data screen will appear.
5. In the above data screen type security.mixed_content.block_active_content in search bar and press enter key.
6. The following data screen will appear.
7. Right click over the filtered value and a menu will appear.
8. Select Toggle in that menu.
9. The values will changed as shown in the below screen.
10. After finishing the above mentioned steps close your browser and re-start it.