What a drama with filesize! =))
Write the full number of Bytes then, in such cases of extreme importance...
The reason is:
1 KiloByte is actually = 1024 Bytes, 1 MegaByte = 1024 KB, and so on.
Some progs consider 1KB = 1000 Bytes.
One of the examples of such a software is DivX coder.
Another example is "DVD size trick" - recordable disks display 4.7 GigaBytes capasity written on the cover. But they really do have 4.3 GB capacity. The "hocus-pocus" - those "4.7" numbers are actually standing for 4,700,000,000 Bytes.
Some progs display approximated filesize. And "ways of approximation" differ.
So practically you can get either 7.88 or 7.52 MB size for one file from different programs.
The good example here is ReGet, Explorer and FAR.
Speaking about firefox - it's safe to say "it was thinking of" something about 8100000 Bytes.
So, as I said, if high exactness is needed - refer to the size in Bytes, for it can't deviate.
Take care!