I have been using Firefox for years now and have no problems with SI or downloads. When i want to download a sermon i simply use (one of the "add-ons") DownThemAll.
I right click the sermon or sermon link and send it to my documents for instance then when it's done (usual in a few seconds) i go to my documents and it's there. Then double click and it comes up or, from "DownThemAll" after it's been downloaded i can just double click right there and it will come up.
I've never had a problem with SI and Firefox ever. Hope this helps. If i can help in any other way, let me know. By the way; i do download directly from Firefox. I never ever use IE for anything except for windows updates and then only do i use the (add-on) IE tab, but thats all.
I have not been nor am i at all having any problems with the crashing of SI using Firefox. Everything has been and still is doing fine and i have the recent updates as well.
Brother Julian