I would be careful around using the non-prefixed and -moz prefix's as they may cause undesired results on desktop browsers
On which browser does 100% cause undesired results?
Interesting. I guess I'll have to revisit 100%, as I found it didn't do much when I tested it a while back (I was still getting the ugly, random text resizing in mobile Safari).
On which WebKit browser specifically does 100% not work properly?
While it may not break on desktop browsers now Chrome may implement it into their Blink engine soon but until someone does implement it the property is safe to use.
Even once it is implemented on desktop browsers, "100%" should still be safe since it only defines a starting point for text size, unlike "none". That is unless the spec changes.