I recently signed up for the Bing Webmaster Tools and it prompted me to install Silverlight. I thought: "That's kind of weird... I'm pretty sure I've got Silverlight... I mean Netflix..." but I installed it, restarted my browser and... it prompted me to install Silverlight again. Okay, Silverlight doesn't work with the Firefox 4 beta, duely noted. It not working with a Firefox beta is legitimate legitimate. Even if someone in the depths of the bat-cave in Redmond has Silverlight binaries that work against the current Firefox betas, I can see not releasing them until it RC's. I get it, but it's still a lame user-experiance.
I switched to Chrome, and then the real page actually rendered. Good. I started pokeing around and land on a page with a scroll bar so I tried to scroll down... and nothing happened. I tried again, nothing. I looked closer. The scroll bars are wrong, text selection doesn't work, neither does Ctrl+Click, and the text is just wrong. It's kind of noisy. At this point that I realize that the whole page is Silverlight rather than just the graphs and fancy bits.
The Take Home Lesson
Don't try to make you're alien rectangle of joy do what HTML does.
Embrace your platform. Don't try to build around it, lest you end up re-implementing it poorly.