I don't know JQuery and don't use it, because I've started learning JS around 1.5 years ago, and at that point standard library was so good that you don't need any libraries for basic DOM manipulation.
It's good, but with jQuery and linter, you'll code faster.
The ";" was inserted by my linter, it's still valid Javascript, so I didn't bother to remove it. It can help if someone will copypaste this code into a bigger userscript, for example.
Good point and after quick search, looks like some people/library use this practice.