OSLO (Reuters) - Norway's minority government proposed on Thursday to temporarily change tax rules for oil firms in a bid to prevent a collapse in investments amid the COVID-19 pandemic, Prime Minister Erna Solberg said on Thursday.The plan could boost the liquidity of oil firms by as much as 100 billion Norwegian crowns ($9.7 billion) combined for 2020 and 2021, by allowing faster write-offs of investments, and thus effectively postponing tax payments until later years, she said.Norway is..