That button is supposed to install an app from the google Chrome store using the following link:
https://chrome.google.com/webstore/detail/khhckppjhonfmcpegdjdibmngahahhckI looked at the page code, and in general it should load the link, go to the Chrome store page for that app. Did not try to chase down the eBay JavaScript that should be making the button work, but that's not relevant - the problem for me, and probably you is that that eBay script that provides the button's functionality isn't working in either of our browsers.
When the button is clicked in Firefox 31 it does nothing, but that is likely because most buttons like that no longer work in FF31 and other older versions. (Button doesn't work in Firefox 52 either, but the page throws up a "you need to install Chrome to install the eBay app an link to install Chrome - that logic may be disabling the button in FF52, and that may be a clue as to why it is dead in FF31, and maybe in your Chrome version - looks like that eBay page checks the browser and may only activate the button if the browser is acceptable brand and version)
You should be able to use the link above to install the app/addon directly. I used that link in FF31, it took me to the Chrome store, page for that app, but popped up a banner that I needed Chrome to be able to install that app (duh!)
If that doesn't work than maybe your version of Chrome isn't compatible with the app (your Chrome doesn't appear to be new enough for eBay as evidenced by that button not working)
