Thumbnails disappear when i change category ...

Hello,
Xhat i did ths morning ...
On my local server (mamp), i installed a new joomla 3.3.6 and JCE editor 2.4.3
I installed all of this by default and added jce mediabox.

At this time, i created a new article with an image in frontend. When i made modification in frontend nothing changed in URL of the image (relative url like images/...)

On second time, i installed flexicontent by default. I only clicked on configuration button without change anything.

Then when i modified old articles of this new site, the relatives URL (i don't use absolute URL)had changed to be for example : /mydomain/images/...
if i created a local site at http://localhost:8888/mydomain/

Then i suppose tht someting's wrong but i don't know what ...
I'll try to install a new site on besace.info to understand (but i lost my parameters ...)

Did you see that befor ?