Running Firefox with user_pref("layout.css.devPixelsPerPx", '2.0'); triggers JavaScript error: chrome://browser/content/browser.js, line 12304: ele is null At http://hg.mozilla.org/mozilla-central/annotate/beca57e612fd/browser/base/content/browser.js#l5033 (This is on a non-Retina MBP, running Mac OS X 10.7.) Probably a regression from bug 647216, which enabled CAN_DRAW_IN_TITLEBAR on Mac.

It's probably because there is no appmenu-button on OSX, http://hg.mozilla.org/mozilla-central/annotate/beca57e612fd/browser/base/content/browser.js#l5039

Yep, I'd buy that.

This seems to do the job, but I'd like to do more testing with it first. I'll request review tomorrow.

Comment on attachment 711545 [details] [diff] [review] Patch v1 > let appmenuButtonBox = $("appmenu-button-container"); > let captionButtonsBox = $("titlebar-buttonbox"); >+#ifdef MENUBAR_CAN_AUTOHIDE > this._sizePlaceholder("appmenu-button", rect(appmenuButtonBox).width); >+#endif Please declare appmenuButtonBox depending on MENUBAR_CAN_AUTOHIDE as well.

Done.

Comment on attachment 711845 [details] [diff] [review] Patch v2 >+ let captionButtonsBox = $("titlebar-buttonbox"); >+#ifdef MENUBAR_CAN_AUTOHIDE > let appmenuButtonBox = $("appmenu-button-container"); >- let captionButtonsBox = $("titlebar-buttonbox"); > this._sizePlaceholder("appmenu-button", rect(appmenuButtonBox).width); >+#endif > this._sizePlaceholder("caption-buttons", rect(captionButtonsBox).width); And now move the captionButtonsBox declaration down such that this code is ordered nicely ;)

Good call. Thanks. :)