If it is a third party pdf browser plug-in, then it will not be a 3rd party Adobe Reader plug-in, since it won't be made by Adobe. There are several third party pdf browser plug-ins. The choice of using them is yours.
I guess I did not phrase my question as clearly as I should. I have a 3rd Party plug-in that I use when I open PDFs in Adobe Reader. Can I have that same plug-in available when I open a PDF in a browser (IE) or do plug-ins have to be specially designed to work within a browser?