Hi, chscag.
Thank you for your suggestions. I must admit that I’m a surface user only of Mac, so I don’t know how to investigate whether I have extensions or plugins. I have a rudimentary knowledge of plugins, and know that I (may) have permitted installation of plugins in the course of time, but not any connected with music, I’m sure. Can I use Finder to locate them? Do they have a special file extension? Can you give me any suggestions how I shall seek further evidence? I can inform you that I don’t use Itunes at all. Any help appreciated.
I have found that other users have had the same problem as myself. See the post from ccviot in the forum Web Design and Housing (2012) who describes exactly my own problem, but don’t seems to have got the problem solved (?), or the post from ekologik on OSX-Apps and Games (2009), who likewise didn’t got the problem solved in Mac Forums as far I can see. It looks a little disappointing.
I see on the internet that Google Crome is able to block up all plugins. Is that a possibility for me to use? It may ruin the useful plugins, but they may be installed individually afterwards, I assume.