If you're anything like me, then you open new links in tabs. Sometimes, if the link has been open for a while, you forget what page you were on when you clicked the link. The back button is disabled since you are in a new tab.
To get around this issue, I use a simple bookmarklet that takes me back to the document referrer. I place the bookmarklet underneath my back button, so I have easy access to it.
Here's a screenshot of a disabled back button (in a new tab):
Here's a screenshot of my browser with the "referrer" bookmarklet:
To install the bookmarklet, drag this link to your bookmark toolbar:
All the bookmarklet does is:
document.location = document.referrer;