We would have to see more of your CSS and mark up to be able to know what the specific issue is.
First of all, you are aware that this is not very IE friendly, right?
FF is using the slashes as end of words while Chr is using dashes, that's why it's "splitting it up" like you described. this MAY BE solved by adding white-space:nowrap; and a max-length to your rule.
since the :after pseudo element is inline, your padding and border are not be affecting the spacing the way you may be thinking. you could add display:inline-block; and see if that is more what intended.. or recalculate the added padding.
Now about positioning, you could add position:relative; to the parent LINK(A tag) and hten use position absolute on your rule control the placement of the URL. However, since the URL content would be out of the normal flow, this would cause it to behave more like a tool-tip.. and I dont know if that was your intent.
I hope this helps.