I'm not sure I necessarily agree with Opera changing their browser.js file to falsely identify themselves as Firefox. For a start, when CVS check their visitors stats, they'll be thinking, "Well, nobody uses Opera so why the hell should we support it?"

BTW, to test what your site looks like to Google, you should really be changing your user-agent too just in case one of your developers is checking for user-agents that he knows work and then modifying the content based on that... which is actually what's happening here. Although they're including client-side browser-sniffing scripts, they actually write the following line to the page for "non-supported" browsers if you go directly to one of their pages:

<meta http-equiv="refresh" content="0; url=/upgrade.htm">

Furthermore, they're including different stylesheets based on your browser too.

No matter what is happening here, if my last name was "CVS" someone would be fired over this issue! Weird it works in Lynx...

At home, I am a full-time Opera user. It is simply the best browser ever created. At work, I have to choose between pukey Firefox or pin-striped IE. Blaaarrrgggh!

What if Opera collected stats for situations like this and made them available to specific site owners like CVS? I guess people would have to agree and all that, but could this be a better situation than if CVS and other sites have reason to believe no-one in the world uses Opera?

I wish all the sites would support Opera. It's my preferred browser of choice.

Just wanted to mention the site doesn't work with Opera Mobile either. That really is a pretty stupid policy...it'd be more useful to give your customers even a half-functional page than nothing at all.

And as has been mentioned, I don't think the workaround they're using to act like Firefox on certain sites is a good idea either. Inflating Firefox stats while removing Opera hits is not a good idea. Instead they could use the same list of sites to conditionally show the Opera user a message encouraging them to contact the site owners and request Opera support. That way if there is enough demand, the site owners would be made aware of it.

It really is baffling that CVS is blocking Opera users when the page could render for them.

Likely the developers of CVS.com had used some proprietary technology to feed web pages to web clients. They might have used such algorithm.
If client == IE then
   FeedPagesOptimizedFor(IE)
else if client == Firefox then
   FeedPagesOptimizedFor(Firefox)
else
   FeedPagesOptimizedFor(null)

function FeedPagesOptimizedFor(client)
begin
...
   if client == null then
   FeedErrorPage;
...
end;

Why didn't they just feed pages without optimization to else-browsers?

Pity
I love Opera
If it would been OS it would of beaten IE and FF by far