Hi,
Ok, I've found the culprit.
The problem come in the fact that I loaded all the jqgrid javascript libraries at the beginning
of my page, in the head element.
I just changed the place of the tags (only the jqgrid's, without jquery), put
them at the very end of my page, just before the closing body tag .
Now It works perfectly on all my browsers…
Cordially,
Geoffroy