Hope your day is going well...
  
  Some potential reasons why your firefox browser might use 60% of your CPU might be as follows: you 
  have an old version of CPU that can only do serial programming, you have an old version of browser that
  slowly and lags at reading each webpage/tab you open that might cause extra RAM memory in CPU. 
  To avoid this issue, I would encourage you to go to the following options depending on what problems (
   above listed) you have: try going to the "about:performance" in the Firefox address bar which will show
   you a list of tabs and how much memory it uses (can also do this in Task Manager [Windows] or Activity
   Monitor [Mac]), refresh Firefox to return to default settings (can navigate "Refresh" via "about:support).
   
   If this problem persists, please don't hesitate to reach out to me sir

Hey Mr. Alija, Hope your day is going well... Some potential reasons why your firefox browser might use 60% of your CPU might be as follows: you have an old version of CPU that can only do serial programming, you have an old version of browser that slowly and lags at reading each webpage/tab you open that might cause extra RAM memory in CPU. To avoid this issue, I would encourage you to go to the following options depending on what problems ( above listed) you have: try going to the "about:performance" in the Firefox address bar which will show you a list of tabs and how much memory it uses (can also do this in Task Manager [Windows] or Activity Monitor [Mac]), refresh Firefox to return to default settings (can navigate "Refresh" via "about:support). If this problem persists, please don't hesitate to reach out to me sir Sincerely, Tharakram.