Ubuntu is more graphical in nature than other linux distros. So it will consume more GPU power and besides that you should have also mentioned your system config since that would have given us more info on your system performance. Low end CPUs generally get high temperature quicker. You can try using another browser to see if the results are the same.
If the problem persists then try reinstalling the OS. Make sure to backup your data if you reinstall the OS.
Also, you can use a tool called "Glances" which is available for Ubuntu to see a detailed analysis on CPU and GPU temperatures.