Plugin problem with Firefox 4

Hello

I have a plugin which loads separate DLL with LoadLibrary() Windows
API.
It works OK up to Firefox 3.6.x but somehow LoadLibrary() call fails
(return NULL) in Firefox 4.
In the plugin code there is _chdir() call to move to the directory
where the DLL to load exists, but looks like the current directory is
not contained in the DLL search.

There is a workaround for this, use LoadLibraryEx() to explicitly set
DLL search path, but wondering why the issue happened. Whatever
changed about plugin in Firefox 4?