Why jpg files are saved with the extension .jpeg instead of .jpg?

Recently, on macOS after updating Mozilla Firefox to the versions above 50, save images of JPG format occurs with the addition of extensions .jpeg.
Many applications do not perceive this extension. It's annoying, as it was before .jpg

Can someone faced? Tried the following:
1) Loading without add-ons
2) Delete or edit the mimeType
3) Create a new profile
August 23rd 19 at 10:30
1 answer
August 23rd 19 at 10:32
You tried to rollback to version Mozilla below 50, maybe it is all about?
Yes...I'm afraid the only thing that will help - Marilou.Konopels commented on August 23rd 19 at 10:35
: checked. Version 49.0.2 even without this bug. So it's in the new versions - Marilou.Konopels commented on August 23rd 19 at 10:38

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