I posted on this subject about a month ago, so you have had some warning of this coming. But now, all support for the align= attribute in XUL with values "vertical" and "horizontal" is removed from both CSS and C++. If you have not changed to orient="vertical" or orient="horizontal", now is the time to do it. It works exactly the same way; it just requires a simple search and replace. "[A]nd there was much rejoicing!" to quote David Hyatt. :) This change was checked in last night and will affect any builds from August 8th on. This has been your daily XUL Syntax update. Next up, more changes from hyatt and probably the removal of <titledbox>. :)
