Browsers change layout engines from time to time so it can be tedious to compare one browser with another. According to this Wikipedia article
up to version 37 Chrome used the same Webkit
layout engine as Safari but since then they have switched to the same Blink layout engine
that Opera has used since Opera 15. Of course Firefox uses the Gecko layout engine
developed by Mozilla.
as does Opera since version 15. Spider Monkey
Wikipedia has a Comparison of layout engines (ECMAScript
page. Since ECMAScript was a Mozilla brainchild it is not surprising that the broadest ECMAScript support is found in the Gecko layout engine used in the FireFox, SeaMonkey, and Camino browsers. So if all else fails on the site you are trying to access I would recommend you try one of those three. Taking the chart of layout and ECMAScript engines together with the browser versions that will run on your Mac you should be able to deduce the various combinations of layout and ECMAScript engines available to you. Unfortunately because of your somewhat elderly version of OS X, the site may be using an ECMAScript command or option that is not supported in any browser/layout engine/ECMAScript interpreter that will run on your Mac. What was it Virtual1 said in another thread about "...dragged kicking and screaming into the present"?