FileZilla Forums

I have been using FileZilla on and off for a couple of years with my MacOS 10.12.6
Now I receive the message above saying I require MAcOS 10.13. I have not upgraded FileZilla and can not see what version I have.
Apple will not let me upgrade the OS for free so now I can't edit a webpage I administer.
What happened? Did FileZilla upgrade itself without telling me?
What can I do? Downgrade? How?

Nils

Addendum:
It turns out MacKeeper, that I tested for fun, updated a lot of programs as a default.
Don't use that program!
The question remains - What to do?
I've tried downgrading to earlier versions of Filezilla but they won't run:
EXC_CRASH (Code Signature Invalid)
Namespace CODESIGNING, Code 0x1

For quite a while now we haven't supported macOS earlier than 10.13

Don't know why it says the code signature is invalid if you use older versions. Maybe some expired or missing certificate on that old version of macOS? Unfortunately macOS is extremely tight-lipped in case of errors.