Zhongwen Chrome Extension
The free Zhongwen Chrome extension is easy to use. Simply download the extension and activate it whenever you are on a site with Chinese characters — both traditional and simplified. When you hover over a character, you will see a pop up with several definitions.
At first, it seems like this is all Zhongwen has to offer, but one quick glance at the keyboard shortcuts popup will tell you differently. You can add words to a wordlist (and export that list to Anki), directly add words to Skritter flashcards, or open a quick shortcut to dictionary sites like Forvo and Line. The shortcut list is a bit finicky, so you may have to click the Zhongwen extension icon and take a screenshot to remember what each key does.
Unfortunately, the app can’t translate full sentences, and sometimes when characters are part of a hyperlink you can only receive the definition of the first word. Nevertheless, Zhongwen is a free app that can improve your Chinese reading experience.
Readlang is a similar application that has less thorough definitions, but it allows you to translate full sentences (although this is a paid feature). With Readlang, the translations will remain on the screen until you intentionally remove them. Both of these apps can be used together depending on your needs.