I am running XP SP3 and FF 3.6.18. I have been having trouble opening PDFs in FF but not in other browsers. FF tells me to update my Adobe PDF plug-in. I click in the FF list to update, go through the procedure and when I click on run I get the following message: "Internet Explorer script error," although I am not running IE and I have no other applications open or running other than Avast anti-virus. The pane gives me two options to the question "Do you want to continue running scripts on this page?": Yes or No. After clicking on either, the pane disappears, but nothing further happens. I have then downloaded the plug-in again, but when trying to run it I get the message: "Only a single instance of this application can run." I have tried downloading the plug-in to a different folder but get the same message. I have also turned off Avast with no change in the above. Now no PDFs open in FF. What to do? Thanks.