Hi, there!
Dear friend firstly I would have to know what message your pc shows when you try to log on to facebook or hi5 or twitter. Without knowing the issue I am unable to solve your issue.
There are lots of possibilities like you said due to your old version of Mozilla Firefox it could happen or may be your internet explorer is crashed or may be you do not have enough memory (RAM) to run facebook, hi5 or twitter on your machine.
You are not getting connection of Facebook, hi5 or tweeter. Firstly you have to make sure that your account is not compromised or blocked. If you are a victim of this illegal deeds you cannot login to these sites. You can try this solution. Clear the all history of your internet browser. You can delete your browser and re-setup it.
I hope the problem will be solved. If still problem occurs re-setup your windows and install an internet security. You can buy internet security or download it. But Buying is better than free downloading. I hope you have got the answer of your question. I hope this will help you.
