Finally got the multi-tab trick to work in Firefox [4 times then it stopped working]. New checkout with credit card is what finally worked for me. Previously wouldn't work for me with Gift Card. Hope that helps someone else.
I know people have had luck with multi-tab in Chrome too but I still have a balance with Gift Card in there. When that's used up I'll try the credit card/multi-tab in there also and post back.
Good luck!