A problem of firefox running on linux (gentoo)

As you can see from the below picture, I don't know why I can only view the simplified version of Yahoo! But I am already using latest version of firefox . And it is ok when I surf other websites.
Any help given would be appreciated:)

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I have solved the problem la.
The problem was caused by installing two versions of firefox which are mozilla-firefox and mozilla-firefox-bin respectively.

This problem will be happened when I used mozilla-firefox so I decided uninstall mozilla-firefox and use mozilla-firefox-bin only. Then the problem was solved.

Thus, it is highly recommended to use mozilla-firefox-bin instead of mozilla-firefox.