Avoid Firefox icons in ESR60

In TBB/ESR60, the browser icon in the top-left of the browser window (at least on Linux) is the Firefox icon. That's because some new Firefox image files were introduced in ESR60 and we aren't properly overwriting them with the Tor Browser icon in our legacy/trac#2176 (closed) patch.

(Note that all these images will be again replaced in the future by a legacy/trac#25693 (moved) patch.)

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