Are you sure it's not some sort of Arabic? Like in the screenshot below, the lower parts of the two browsers might look the same at first sight, but for someone who reads Arabic are actually quite different.
You might be running into an issue with Apple Advanced Technology versus Microsoft OpenType. Some details from "Arabic fonts for the Mac - further detail":
The technology that allows automatic context analysis - that makes an isolate "b" turn into an initial b when you add another character to it - is linked to the font, and can in OS X be of two different types: One is Apple's own which is called AAT, for "Apple Advanced Technology". The other is the one mentioned above, called OpenType.
This, incidentally, is why Safari suddenly stops displaying Arabic properly when you install Microsoft Office 2004: That also installs versions of Arial and Times New Roman that contains Arabic characters, but in OpenType format (as in Windows). Web pages will routinely ask for Times New Roman even for Arabic text, and as it exists on your machine and contains Arabic characters, Safari will go ahead and display those. But because this (Microsoft) font is based on OpenType, the Arabic letters it contains do not combine into words. You must dump the Microsoft version of these two fonts, and replace them with the older, Apple, version of the same fonts, which did not have any Arabic. Safari will then pick another, working, Arabic font to display the text of the website. -- Firefox, which supports OpenType ligatures, and other browsers do not have this issue.
Below, see Safari on the left and Firefox on the right, when the Microsoft OpenType Arial font has been installed (in 2008 OS X and browser versions):