Simple THighlighter от Achintya Sharma

follow these steps to use:
1. Install the extension from firefox Add-ons.
2. To highlight, just click any text with your mouse and that should automatically highlight the text.
3. To remove the highlight, just tap the highlighted text once and that should remove it.

You can find the source code, from my github repo:
https://github.com/sharmaachintya08/Highlighter-firefox