When dual screen, Firefox changes of screen when opening an url from another apps not in the same viewport

Step to reproduce:
- Be in dual screen with screen A and B
- have several viewport (tested with 4 viewports in square)
- Put the launcher in screen A
- Put firefox in screen B
- Click on a url from another applications not in the same viewport (I tested with Liferea and Xchat-gnome).

Expected :
- The icon of firefox wiggles in the launcher
- Firefox opens the url
- Firefox stays in screen B

Actual :
- The icon of firefox wiggles in the launcher
- Firefox opens the url
- Firefox magically jumps to screen A (which is the primary in my case)