I'm not sure that I understand how you see that scrolling text on that page.

Do you see that text double on two lines?

Can you attach a screenshot?

Use a compressed image type like PNG or JPG to save the screenshot and make sure that you do not exceed the maximum file size (1 MB).
Make sure that you choose an unique name for the image to avoid problems with an already existing image with the same name.

Clear the cache and remove the cookies from websites that cause problems
Outils > Options > Avancé > Réseau > Cache > Vider le cache maintenant
Outils > Options > Vie privée > Cookies > Afficher les cookies

Start Firefox in Diagnose Firefox issues using Troubleshoot Mode to check if one of your add-ons is causing your problem (switch to the DEFAULT theme: Outils > Modules Complémentaires).

See Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems and Troubleshoot issues with plugins like Flash or Java to fix common Firefox problems

ci joint une capture de l'écran incriminé

J'ai suivi vos conseils concernant cache et cookies et ai testé le mode sans échec avant de revenir au mode normal; le problème semble résolu lorsque j'ouvre firefox et me connecte sur le site..merci..pouvez vous me donner une explication du problème? cordialement, yk