Eight <filename.###> Files In My \roaming Folder

I am using Firefox 43 on a Windows Vista SP2 system. On October 22, 2915, something put 8 files, all 2048 bytes long, in a folder named ".#" in \roaming. They are named:

MBX@1440@2BA1C18.###
MBX@1440@2BA1C28.###
MBX@1440@2BA1C38.###
MBX@1440@2BA1C48.###
MBX@DD0@2991C18.###
MBX@DD0@2991C28.###
MBX@DD0@2991C38.###
MBX@DD0@2991C48.###

They are dynamic link files. I would like to know what these files do, where they came from, and if they are dangerous and should be removed.

Thank you.