It sounds like there is an infinite loop in your code. An infinite loop will run until your browser gives up waiting for it to finish.
Usually, it is just the one tab that is affected. Close or reload that tab. Then, work on fixing the code before you submit it again. Most likely it is a tiny mistake. Look closely at any loops you have included in your code. Don't worry, you aren't hurting anything if you crash again although any unsaved code will be lost.
If you are having trouble finding the mistake on your own, you can get help by visiting the lesson's Q&A Forum.