OSLO (Reuters) - Norway proposed on Thursday to temporarily ease tax rules for oil firms to try to prevent a collapse in investments due to the coronavirus pandemic and a related collapse in crude prices.The plan could boost the liquidity of oil companies by as much as 100 billion Norwegian crowns (7.77 billion pounds)over 2020 and 2021, Prime Minister Erna Solberg said. The companies will be allowed to write-off investments more quickly, effectively postponing tax payments until later..