Visit https://addons.mozilla.org/en-US/firefox/addon/bahai-reference-library-wik/ and click "Add to Firefox".
Not currently available for Firefox Mobile.
I am awaiting approval via the Safari Extensions Gallery, but for now you can follow these instructions:
Visit the Chrome web store page and follow the instructions there to install.
Visit the Opera extensions repository and follow the instructions there to add to Opera.
I hereby release all of these add-ons under the MIT license (so the software is thus free as in "free coffee" and as in "freedom").
Let me know at firstname.lastname@example.org if you have any issues or feedback.