Ah, keyboard shortcuts.

I'm too used to using vim, where Ctrl-w deletes the preceding word in insert mode. (The same shortcut works in the terminal and other places, as well.) The downside is that when I'm on a Windows machine, i.e. using Firefox at the library, trying to delete a word reflexively closes the window in which I'm typing. This has happened three times already and almost happened once while typing in this post.