Rated 4 out of 5 stars
Very good extension/add-on, can't live without it.
However, I'm using Waterfox since I want to take advantage of the 64-Bit technology (speed, performance, etc.) since there's only 32-Bit Firefox (except the Nightlies), and HTML Validator doesn't work anymore.
Any idea when we could expect a 64-Bit-compatible version of this add-on?