We are not aware of such a prolem with RadToolTip and you can also see that in the common case everything works under all browsers including FF - you can check this by examining our online demos below:
That is why I believe that there is something specific in your case which causes this problem. In order to be able to help I will really need to examine a sample demo. Please prepare a very simple demo e.g a hyperlink which is a target and it is tooltipified with simple sample content for the tooltip. Once you make sure that the setup is fully runnable and reproduces the issue, share the full source code here along with detailed explanations and I will build a test demo, debug it locally and help you resolve the problem.
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