hello and welcome to justanswer, My name is ***** ***** i will be assisting you today,
I' am sorry about the issue, to Stop flickering in mozilla firefox please follow these steps :
1. Open Mozilla Firefox, click on Firefox Menu button and select "Options".
2. Go to "Advanced" tab and disable "Use hardware acceleration when available" option.
If you are watching videos on youtube please enable HTML5 on your firefox browser :
https://www.youtube.com/html5 and click on request The HTML5 player
there is no 'options' under the firefox menu.
Ok Please follow again these stepsThank you