What version is it at now? I thought I read somewhere you can't make the leap from a very old to the very new. Don't recall the numbers.
Also, give Edge/Chrome or even IE a try. I've had some really wonky things going on with FF myself lately. Both with download and file uploads. I think they may have a bug.
Current firmware 2.13
Tried IE. No go.
Problem is in the name of file. You have quite old firmware. When WiFiLogger2 was released I have change some little things.
Your firmware name of the file should be WiFiLogger2????.bin and you have WiFiLogger_????.bin
Please just add 2 after r and update will pass.
You can also update using update system. If you don't have update button in SETUP -> SYSTEM
then try to open
http://WFL_IP/updatethere is extreme simple menu to make firmware update.