https://www.waterfoxproject.org/update/osx64/56.2.7/en-US/release/update.xml at the time of writing:
<?xml version="1.0"?>
<updates>
<update type="major" appVersion="56.2.7.1" buildID="20190201223501" detailsURL="https://www.waterfoxproject.org/blog/waterfox-56.2.7-release-download" displayVersion="56.2.7.1" extensionVersion="56.2.7.1" platformVersion="56.2.7.1" version="56.2.7.1">
<patch type="complete" URL="https://storage-waterfox.netdna-ssl.com/releases/osx64/update/waterfox-56.2.7.1.en-US.osx64.complete.xz.mar" hashFunction="SHA512" hashValue="3872f991fd688413b91005f07b753fdc361032276d35f4006bd66089a484cf4ccaa718bff00131367117d172c14f766e5db3444fac2aa706bee02cc5f2411351" size="83909941"/>
</update>
</updates>
@MrAlex94 compare the first line above with the first line of the …/56.2.7/en-US/release/update.xml files for other platforms.
Meta/tracking: #582
Cross references:
Additional information for end users on Macs: this is, as far as I can tell, a harmless cosmetic issue.
Where the two versions in the dialogue are the same, for example:

– you may ignore the Update to … button.
Fixed!
https://www.waterfoxproject.org/update/osx64/56.2.7/en-US/release/update.xml?force=1
<?xml version="1.0"?>
<updates>
<update type="major" appVersion="56.2.7" buildID="20190201223501" detailsURL="https://www.waterfoxproject.org/blog/waterfox-56.2.7-release-download" displayVersion="56.2.7.1" extensionVersion="56.2.7" platformVersion="56.2.7" version="56.2.7">
<patch type="complete" URL="https://storage-waterfox.netdna-ssl.com/releases/osx64/update/waterfox-56.2.7.1.en-US.osx64.complete.xz.mar" hashFunction="SHA512" hashValue="3872f991fd688413b91005f07b753fdc361032276d35f4006bd66089a484cf4ccaa718bff00131367117d172c14f766e5db3444fac2aa706bee02cc5f2411351" size="83909941"/>
</update>
</updates>
Most helpful comment
Fixed!
https://www.waterfoxproject.org/update/osx64/56.2.7/en-US/release/update.xml?force=1
<?xml version="1.0"?> <updates> <update type="major" appVersion="56.2.7" buildID="20190201223501" detailsURL="https://www.waterfoxproject.org/blog/waterfox-56.2.7-release-download" displayVersion="56.2.7.1" extensionVersion="56.2.7" platformVersion="56.2.7" version="56.2.7"> <patch type="complete" URL="https://storage-waterfox.netdna-ssl.com/releases/osx64/update/waterfox-56.2.7.1.en-US.osx64.complete.xz.mar" hashFunction="SHA512" hashValue="3872f991fd688413b91005f07b753fdc361032276d35f4006bd66089a484cf4ccaa718bff00131367117d172c14f766e5db3444fac2aa706bee02cc5f2411351" size="83909941"/> </update> </updates>