Java can become disabled in your broswer (maybe after a Windows update or other update), so here is how to check:
Please make sure you have checked your System Settings first!
Click on the Tools option...
... and select Options...
Now click on the Content icon...
...and make sure that the Enable Java checkbox is ticked.
And thats it!
Click on the Tools option...
... and select Internet Options
Now click on the Advanced tab...
...scroll down the list to Java (Sun)...
...and make sure that the
Use JRE (etc.) checkbox is ticked.
...then this should have solved the problem. Just click OK at the bottom and you are all done.
Please note, however, you may need to restart your PC for it to have an effect.
...then you need to check your Addon Settings...