This is a weird one.
The only iPhone documentation that's readable on an iPhone is the web based iPhone User Guide.
Except it didn't seem to work on my iPhone.
I could click down to any page, but when I tapped the back button I'd get a blank screen. If I force a refresh I'm back at the top menu, rather than the last page I visited.
On the desktop it doesn't render at all in Firefox.
Using Safari on the desktop (much faster!) I was able to figure it out. You have to navigate by the breadcrumb display at page top, the browser back buttons don't work.
I wonder how many people have run into this.
Apple should fix the web page. Breaking browser back buttons is rude.