[Update: As of Chrome version 45, released circa 1st September, 2015, Chrome no longer supports NPAPI at all. ]
In June last year the Google Chrome team announced that they would be ending support for NPAPI based plugins by September 2014. NPAPI is an ageing technology used by, most notably, Java, Silverlight and the Google Earth plugin. It is being dropped largely because it is considered a potential security risk.
In September Google released a 64-bit version of Google Chrome that did not include support for the Google Earth plugin or other NPAPI based plugins. However, the 32-bit version still supported it and has continued to support it. Over time, however, Chrome has been making it increasingly difficult to run NPAPI plugins, requiring the user to explicitly allow a plugin to run before displaying it.
Now, Google has just released Chrome version 42 that drops support for NPAPI plugins by default. It is still possible to get them back is via a Chrome flag, but presumably that option will soon be disabled too.
For now, if you really need the Google Earth plugin in Chrome 32-bit, you can reenable NPAPI by entering the url: chrome://flags/#enable-npapi in the address bar then selecting ‘Enable’ below the ‘Enable NPAPI’ section then relaunch the browser.
The Google Earth plugin itself was deprecated in December and is set to stop working on 12th December 2015.
Firefox is also slowly phasing out NPAPI plugins and as far as we know the latest Internet Explorer only allows them in the 32 bit version in compatibility mode and not at all in the 64-bit version.