Media folder not accessible

[Blaise15]

Hi
I am fiddling with a Joomla! 1.6.1 site on a MacBook, OS X, in local using MAMP and Firefox 4.0.

Using the Media manager within Joomla!, I could not create a new folder. I click the button, the screen is refreshed but no new folder is displayed. So I used the Finder to make a new folder (htdocs/mysite/images/NewFolder). I can now see that folder from the media manager.

I can see it, but I cannot open it.
When I try to open it from within Joomla!'s Media manager, I get a brand new behaviour from Firefox.
The two pictogram pointed by arrows in the image attached act like if ... something was hindering their rotation.

If I do move to an other option in the menu, their "start and stop" behaviour will continue forever, I think, but the file will not open.

I get the same behaviour with a Beez or a Desertlab template.

I suppose it is a bug... Is it ?

Thanks a lot !
B.