Add :only.

vimperator/locale/en-US/browsing.txt

@@ -323,6 +323,13 @@ Close window.
 ________________________________________________________________________________
 
 
+|:on| |:only|
+||:on[ly]||
+________________________________________________________________________________
+Close all other windows.
+________________________________________________________________________________
+
+
 |:xa| |:xall| |:wq| |:wqa| |:wqall|
 ||:wqa[ll]|| +
 ||:xa[ll]||

vimperator/locale/en-US/index.txt

@@ -221,6 +221,7 @@ section::Ex{nbsp}commands[ex-cmd-index,:index]
 ||[c]:nohlsearch[c]|| Remove the search highlighting +
 ||[c]:noremap[c]|| Map a key sequence without remapping keys +
 ||[c]:normal[c]|| Execute Normal mode commands +
+||[c]:only[c]|| Close all other windows +
 ||[c]:open[c]|| Open one or more URLs in the current tab +
 ||[c]:optionusage[c]|| List all options with a short description +
 ||[c]:pageinfo[c]|| Show various page information +