"Navigation to the webpage was cancelled"

A while ago, when I tried to open pdfs sent to me by email, they defaulted to opening in IE not in Acrobat on my PC.  I was able to find the solution online and have had no problems since then.  I believe the problem arose following an update to IE (I use Firefox).

I've just begun a new job, and had the same problem, so applied the same solution.  Since then, each time I open a new pdf I get an error message which says "Navigation to the webpage was cancelled.  What you can try: retype the address."  Nonsensical, because I haven't typed an address.  I've only been there one day, and it happened the first time I opened each pdf for the first time.  If I later had to re-open the same document there was no error message.  If relevant, IE is not the default browser (they use Chrome).

I've searched for a solution, but all references to this error message seem to be years old, and do not relate specifically to pdfs.

Does anyone have any ideas please?