Firefox crashing in Catalina

Ever since I upgraded to Catalina on Friday the 18th October I cannot open Firefox. I get a box telling me that there is another copy of Firefox open and to close it. It then just hangs indefinitely. Judging by the fact there is no great outcry to be found when googling this I presume it is just something individual to my iMac, which is a late 2012 model, the last to be able to upgrade to Catalina. Anyone else having this problem?