Do you have to use Firefox to get this feature. I operate in Windows. Does this mean I can't get this feature?
There isn't an absolute yes/no answer. The little pop-up displaying the meaning of an acronym is implemented using the HTML <ACRONYM> tag. Your broswer has to recognize this tag in order for that feature to work. It isn't exactly a forum feature, except that the forum software injects the <ACRONYM> tag when it sees something it recognizes as such.
In Windows, the acronym tag is supported in IE 5.5 and later. I hope you're running a new enough version of Windows to have a much later version of IE than that.
Are you letting the point of your mouse pointer rest on top of the acronyms?
Other browsers, such as Firefox, work on Windows, and also support the acronym tag.