Hi,

for editing and converting vector drawings (such as svg) I always use Adobe Illustrator. You can get a fully functional demo (which shuts down after a month, I think) from the Adobe website. I'm a little surprised firefox won't open svg files with a .svg extension, as far as I know it's been capable of doing that for a long while now. Is there any chance you have a very old version?

Best wishes,

Rutger