Does not work on Firefox with NoScript addon - even if `github.com` is explicitly allowed, and even if NoScript is set to "Allow Scripts Globally (dangerous)", one still gets in Error Console (Ctrl+Shift+J) in Firefox: 

> [NoScript] Blocking nosniff Javascript served from https://raw.github.com/Manishearth/Manish-Codes/master/StackExchange/ThumbnailUpload/ThumbnailUpload.js?rand=16 with wrong type info text/plain, inline and included by http://stackapps.com/questions/3507/thumbnail-uploader

Here is the relevant post from NoScript forums:

[InformAction Forums • View topic - nosniff is blocking a script without telling me](http://forums.informaction.com/viewtopic.php?f=10&t=8112)

> I can't think of any reason why NoScript should block scripts without indicating that it is doing so. It just leads to frustration.  
> [...]  
> Not sure it's worth the effort: careless developers like that will soon be forced adapt, since IE9 doesn't give any visual clue either of this (correct) blocking [...]

Well, that's a shame `:/` ...