Cannot display SVG used by

I'm trying to set up the vector web application on my server http://ift.tt/2dmlNj9 , but I've found that the SVG used by <object> (I think they're generated by javascripts.) cannot be displayed in browser. However, the official app at https://riot.im displays all the SVG files correctly. I made a small test on my server:

http://ift.tt/2dKFGmn

I use <img src="..."/> and <object type="xvg+xml" data="..."></object> to use an svg file, but the browser only shows the <img src="..."> image, the Firefox's Developer tool only says "Could not load the image". Chromium and Qupzilla also fail to load it. If I open the html file locally with file:///some/path/index.html, it works fine.

I've searched on the web, and checked I have set up the MIME type correctly in lighttpd. Can anyone tell me what's the problem?