There's now an official Brackets feature for this, but you have to enable it in your preferences:
- Choose Debug > Open Preferences File in the menu
- Add a new top-level entry
"highlightMatches": true
- Save the file and you're done!
You can also set it to "highlightMatches": {"showToken": true}
if you want it to highlight without even making a selection first (just based on cursor position alone).
More details are available on the preferences documentation page: https://github.com/adobe/brackets/wiki/How-to-Use-Brackets#preferences.