[Javascript] standard !

[Bernu Bernard]

Hi,
I follow this list from a couple a weeks. I have seen on some links  
that the most commonly used browsers are
IE6 (about 80%) Firefox (15%) and the rest (mainly  Opera, Safari,  
IE5) for the last 5%.
Also, it seems that all these browsers use at least javascript 1.2

So if I decide to design a site for say 98% of the browsers (I  
discard IE5), where do I find for what function is supported by all.
I often look at w3chools, but it seems to be not uptodate.
I red the Javascript Reference book from Fanagan (O'Reilly), 4th  
edition from 2002, but Firefox is even not mentioned.

For example, parentNode is in the DOM, but on the thread about "Code  
optimization", Terry says "this.parentNode doesnt seem to work for me".
I found that parentElement also exists.
I tried to build HTML code using template-block by doing this :
document.getElementById 
("thisHTMLBlock").innerHTML=document.getElementById 
("thatHTMLBlock").innerHTML;
which works for <div> or other tags, but will definitively crash  
Safari when changing the text of an <input type="text">

So my question is where can I find informations about writing safe  
javascript that will work.
Any good  book recommandation ? Any site recommandation ?

Any help would be appreciated,

Bernard