Final answer:
If the U.S. dollar weakens, Australian firms selling in the U.S. will lose because their U.S. sales revenue will convert to fewer Australian dollars. Conversely, U.S. firms selling in Europe would likely benefit as their exports become more competitive.
Step-by-step explanation:
If the U.S. dollar weakens, different parties will be affected in various ways. For those who are importing from the U.S., a weaker dollar is actually beneficial because they can get more for their currency, so they will not lose but possibly gain.
For Australian firms selling in the U.S., a weaker dollar could harm their profitability because when they convert their U.S. earnings back into Australian dollars, they receive less than they would have if the dollar had been stronger. U.S firms selling in Europe would benefit from the weakened U.S. dollar as it would make their exports cheaper and potentially increase their sales.
Lastly, Australian firms selling in Japan are not directly affected by the USD currency movements unless there is a significant impact on global currency exchange patterns that affects the Australian dollar in relation to the Japanese yen.
Therefore, the party that would lose from a weakened U.S. dollar, from the mentioned options, is the Australian firms selling in the U.S.