The problem is not the space/new line though, or the specific translation for 'more'. The problem is the length of the complete header, thus including all the other menu items too.
In your translation the menu header showing all the menus is too long, which makes that MSIE searches for any space in it so it can split words to a new line in order to fit the entire header next to the logo. Mozilla doesn't do this (it doesn't split the line), but simply moves the entire line to below...
So you don't really need to find a shorter translation specifically for 'more'. You could try and find a shorter translation for any other menu, if that would be easier. Just as long as the complete menu can be shown next to the logo it would be fine.
Tip: When you've found some shorter translations, test the menu out by clicking on the longest word. Make sure the line fits the space in that case too. This because the active menu item is shown in a bigger font size, enlarging the whole menu bar even more....
Although it is a shame that we don't have more space there... With all respect to Patchou (or Guido), but sometimes he seem to (note: seems to 
) forget that English is a pretty short language and most other languages are quite longer and need far more space to put in the same words (Dutch for example is way longer and we face that problem all the time). Although, I know he knows this issue quite well though. But sometimes... gnaaaa... well, bugger him till he give in, because it is a shame if we can't translate the words properly like they should.
/ 
