Welcome to Linux.org.
Please list your system specs make / model / processor / amount of memory / graphics card or integrated graphics adapter.
Ubuntu is a resource demanding distro and can and will load a processor if the graphics card isn't powerful enough to run Gnome3 user interface.
system H61M-S2-B3What are the specs of your pc/laptop ?
You could also try Chromium browser...it should be located in software manager on 19.1
Are there any other signs of freezing in the pc ?
It sounds very much like either insufficient ram or maybe a slow processor or possibly even a graphics card driver glitch.
Give us some detail...Brand/model/cpu/ram/ etc etc etc