In FireFox, animation starts before div's background appears.
This doen't happend in Chrome and Opera
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Unsolved Mysterious Bug (2018-12-24)
2019-01-01:Solved
In CPreloader.js, function was used as an index of 
the list array. 
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source:COptBg.js
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			CRefCnt.lock();
			CPreloader.loadImgs(urls,this,function(){
				CRefCnt.unlock();
			});

CRefCnt.unlock(); doesn't work but if you just add
" " before or after it, it works.
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Fix
			CRefCnt.lock();
			CPreloader.loadImgs(urls,this,function(){
				CRefCnt.unlock(/* unlock bug fix */);
			});
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