Firefox and many other X applications that support clipboard operations (^X/^C/^V) do not always play well with some other X applications (most notably, xterm). This is because there are several selection types in X. The "select with the mouse and it is there for you" is called PRIMARY selection. The "^C to copy, ^V to paste" one is called, not surprizingly, CLIPBOARD. There can be more, but those two are the ones used the most. The problem is that sometimes when you create a selection in an xterm, you really mean to paste it in an application that pastes from another selection type, and the other way around. Some would argue that having multiple selection types (just names, really) is a fact of life. Some would probably try to persuade you that this distinction is somehow useful. Me, I would just say that it is annoying. So, before trying to hack something up, I googled a bit, and found this page. David Simmons presents a couple of xterm patches, one of which does exactly what I want, making any xterm selection to use both PRIMARY and CLIPBOARD buffers. His patch requires recompiling xterm, although he mentions that the same effect can be achieved with X resources manipulation. David left that part as an exercise to the reader. For the reference, here is the solution. Put the following into your ~/.Xdefaults file: XTerm.vt100.translations: #override\n\   Shift <KeyPress> Select:select-cursor-start() select-cursor-end(PRIMARY, CLIPBOARD, CUT_BUFFER0) \n\   Shift <KeyPress> Insert:insert-selection(PRIMARY, CLIPBOARD, CUT_BUFFER0) \n\   ~Ctrl ~Meta <Btn2Up>:insert-selection(PRIMARY, CLIPBOARD, CUT_BUFFER0) \n\   <BtnUp>:select-end(PRIMARY, CLIPBOARD, CUT_BUFFER0) \n\ Reload your resources with xrdb, or restart your X session. Enjoy.