How to reproduce with Chrome :
- Go to tab "Users, groups and rights"
- clic on button "Right profiles"
- Let this panel opened
- then, select a page on the sitemap panel
- go to tab "page"
- clic on menu "Restrict access"
- let this panel opened
- then, try to add a page in the sitemap
-> 3 behavior possible :
- in the popup the content of the "Right profiles" panel appears
- or the button "add a page" does not work
- or the content on the popup appears in the "Right profiles" panel
See screenshot for more precisions