HTML Regex Data Extractor

This extension is useful for those who want to test the regular expression on the live HTML content.
They can also use their custom content.

Usage :
- Press Alt-R to test with your custom content
- Press Ctrl-U or right-click and choose “View Page Source” to test with HTML source of current page
- When you are viewing the source code, to show/hide the Regular Expression Bar, on Toolbar, choose View -> RegexHTML

Source : here