DumpItBlue is designed to help people extract data from Facebook that typically take many manual, repetitive tasks to do otherwise.
This isn't the first Facebook extracting app we've seen, and they often come with problems, problems that pale in comparison to trying to collect all of YOUR photos, videos, etc. Facebook works pretty hard to keep you from getting your information back.
So, what kind of problems can you expect? You must have Google Chrome. It's an experimental tool and only works as long as it is updated when Facebook is updated and Chrome. It would help if you had good latency from your internet connection to Facebook and with Firefox. There can be some minor issues here if you've ever noticed how annoying Facebook can load sometimes. If you have a FAT32 drive, there may be numerous issues, though those are rarely seen nowadays.
Most importantly, as earlier mentioned, these bugs can come and go depending on Facebook and the current version of DumpItBlue.