.xpi is the extension for Mozilla addons. Place the file in the folder C > Program Files > Mozilla Firefox, and then open Firefox > Files > Open file... , and navigate to & open the same file, and it will install as an addon in Firefox.
You don't need to move the XPI file to Mozilla first - simply use File > Open File and the installation will move it to your profile folder automatically.
Hi Carol,
no, this file would not open until I opened it in FF. The dialog box looked different: instead options to Run or Save, my options were Find or Save. Find as in, find a program online to open it. This was in IE, and I don't user any d/l managers or anything, if this helps.








