scrolling mouse wheel in MozillaFirebird leads to X freezing

[hanzotutu]

I've tried a long time to trace down this problem in my gentoo box.
When I was scrolling the mouse wheel to scroll down the webpage
in Firebird, X may be frozen, though mouse can still move around.
What's the problem? how to solve it? Thanks.

[GentooBox]

what is your cflags ?
what version of firebird ?
kernel ?
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