Katherine Lynch.org

Tabindex can be a very helpful attribute when coding a complexly-structured web form or page for accessibility.  It basically tells a page the order in which elements should be highlighted when the tab key is used.  Remember, lots of assistive technologies use the tab input. 

While coding, I stumbled across this little nugget that I thought I'd share here, thanks to Edward Bilodeau (same guy, new blog).

How to get Firefox/Mac to recognize tab index

I just spent the better part of an hour trying to 
get tabindex to work under Firefox/Mac OS X.  
The solution lies not in Firefox, but in the Mac 
OS X preferences.

Apple Menu > System Preferences > 
Keyboard and Mouse > Keyboard Shortcuts and 
under "Full Keyboard Access" choose "All controls".

Sweet lord....

Link to original

Without this enabled, every page in your browser becomes a keyboard trap.  Very frustrating.  Thanks, Edward!