It's hard to really tell, but it looks like sometime between M10 and M18, xulkey either was implemented, or was _planned_ to be implemented, as a sort of alternative to the modifiers attribute, where you would put |xulkey="ctrl"| on a keyset, and then for individual keys say |xulkey="true"| if you wanted that required as a modifier. The ones I removed from /mail/ in bug 487370 and the ones that live on in /suite/ seem to be from that. Hard to tell, given the timing, whether the ones in inspector are from that, or from a temporary reinvention of it, or what. http://bonsai.mozilla.org/cvsblame.cgi?file=/mozilla/extensions/inspector/resources/content/keysetOverlay.xul&rev=1.2&cvsroot=/cvsroot has some... it's, um... bleah. In any case, at the absolute most it would make only ctrl+F work in a build from somewhere between M10 and M18, while (assuming that xulkey actually was ever implemented) just typing all the other <key>s that don't have an xulkey attribute would perform their action without any modifier.

Comment on attachment 372627 [details] [diff] [review] Fix r=sdwilsh, but please fix the line wrapping on those attributes.