I've already verified that the display is not NULL. I'll try the experiment you suggested though. Thanks. <div class="gmail_quote">2009/2/3 Dan Nicholson <<a href="mailto:dbn.lists@gmail.com">dbn.lists@gmail.com</a>> <blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"><div class="im">On Thu, Jan 29, 2009 at 5:08 PM, Tristan Schmelcher <<a href="mailto:tschmelcher@google.com">tschmelcher@google.com</a>> wrote: > Hello all. Sorry if this is not the right place to send this, but I'm > developing a plugin for Firefox on Linux and I've run up against a > roadblock. In my plugin I'm being passed a pointer to an X "Display" struct > (in NPP_SetWindow, for those of you that know NPAPI) and I'm calling > XtDisplayToApplicationContext on it to get an app context to use in various > Xt calls. Now on most systems this works fine--e.g., Ubuntu Dapper 32-bit > with FF2 and Intrepid 32-bit with FF3 both work flawlessly. However, when I > build a 64-bit version and try it on Ubuntu Hardy 64-bit with FF3, it > doesn't work. When it enters XtDisplayToApplicationContext, I get "Error: > Couldn't find per display information" on the console and the program exits. </div>I think that happens when you pass a NULL Display to XtDisplayToApplicationContext. I can't say I know anything about Xt, but does it fail in a simple testcase? #include <X11/Xlib.h> #include <X11/Intrinsic.h> #include <stdio.h> #include <stdlib.h> int main(int argc, char *argv[]) { Display *dpy; XtAppContext ctx; dpy = XOpenDisplay(NULL); if (!dpy) { fprintf(stderr, "XOpenDisplay failed\n"); exit(1); } ctx = XtDisplayToApplicationContext(dpy); XCloseDisplay(dpy); return 0; } -- Dan </blockquote></div>