…problem solved. It was an element in a hidden container (I think a button) that was pushing the text right. Not sure though why Safari and Google didn’t mind this…
They’re both using the same rendering engine: Webkit. Differences like that between browsers tend to disappear, there was a time it was a nightmare.
In your case, it’s maybe an interpretation of the box model. Webkit decides not to give any dimension to the ghost element because it has no content. For a reason or another, Firefox considers the element and gives it dimensions, so it exist in the ffox version of the page and not on the Webkits.