Rated 5 out of 5 stars
Poor HTMLValidator, poor Marc.
Firefox has problems but all we notice is that an extension is not prepared to cope with the bad attitude of the Firefox-developers.
I love this extension and will rather stop using Firefox than do without HTMLValidator!
Having overcome the worst trouble with the 10.x releases of the browser, I am glad to say, that the extension works fine under Linux 64Bits.
Enjoy is the word. Rated 5 out of 5 stars
What do you want to compare this extension to? Never before had it been so much fun, to bat ones fingers with a heavy tool.
Addition 2007-04-23: No speed problems here.