idea?

Thankfully, if I'm not mistaken, deviantart.com is designed entirely around firefox users, in fact they even have on the front page that the FireFox browser is recommended for the best browsing on their site. Much wootage for DeviantART! :3

Like the others said, that in itself (with the way you make it sound) is an unreasonable strategy. However, if you intentionally made use of web standards MS was too lazy to handle properly – probably not a hard thing to find, really – I think that would be reasonable. My favorite example is semitransparent PNG images, which can have quite an impressive effect when applied in the right places.

Imagine a website designed for IE that offered a "crappier" version for Firefox, that invited you to switch to IE in order to see the site in all its glory.  How would you react?  Would you switch, or would you get angry at the website?

What may work is to offer a decent version for all major browsers and an enhanced version for Firefox.  Offering a poor version for the most-used browser won't accomplish anything... though it may convince people to leave your site for one of the other zillion sites on the Internet.

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Can Firefox users and Opera fans agree on anything?
The Alternative Browser Alliance

It's true that we are here to Spread Firefox, but we are not here to force people to use Firefox because the web page looks awful in IE by design and by use of bullying tactics. Don't give Firefox a bad name by forcing people who visit your website to use Firefox. I certainly wouldn't use a website that favored one browser over another because the webmaster is using bullying tactics to force users to use the browser he thinks is right, no matter if I use that browser or not. Place a Spread Firefox button and/or banner by all means, but don't cause problems by favoring Firefox in your website and making it inaccesable to IE and other browsers.

That said, remember that we are using web standards here. Why don't you just design your page using the set standards, and just have a link at the bottom saying this page is "best viewed with Firefox" and a link, instead of "fixing" it so it doesn't look good in IE anyway? I think that would make your site more favorable.