Look at the picture :

Addons support issues are property of the Addon creator. FF doesn't provide support for addon issues.

PatrickPIGNOL said

Why for add-on module page "version 59(quantum) == version 52" ? Cannot install "foxy proxy basic" add-on cause of this bug !

In your More System Details on right of posts your useragent is showing as Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Firefox/52.0

Perhaps either you or a useragent switcher extension has modified the useragent to show as Firefox 52.0

https://support.mozilla.org/en-US/kb/how-reset-default-user-agent-firefox

However the likely reason is due to the privacy.resistFingerprinting being toggled in about:config from the default in which one of the things this does is change the useragent to show as if you were using Firefox 52.0

Type about:config with a : in Location (address) bar and filter for privacy.resistFingerprinting and right-click this Preference and select Reset.

WestEnd said

Addons support issues are property of the Addon creator. FF doesn't provide support for addon issues.

If the question was not clear enough for you, the image and more system details by OP should have made it clear enough on what was going on.

Basically the OP has Firefox 59.0.2 however the useragent is showing as Firefox 52.0.