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 [...]

Also, cannot cheat by downloading the script locally ([SourceForge.net: MathJax: Greasemonkey script](http://sourceforge.net/projects/mathjax/forums/forum/948700/topic/3701296)):

> Unfortunately, GreaseMonkey will not allow you to load a local file (i.e., a file:// URL), for security reasons. (Personally, I think you should be allowed to authorize specific scripts to be loaded that way, but I didn't write GreaseMonkey, so don't get to make those choices.)

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

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EDIT: Many thanks for the quick update from the author (first saw the update on GitHub, then the response here `:)`); I tried the NoScript version - and indeed, now the toolbar button "T" shows - but the iframe cannot be populated:

![firefox-bad-iframe][1]

I tried to mess with the script locally, and I think the breakage got induced already at `if(iframeWin.$){ \n var script = iframeWin.document.createElement("script");` ... but cannot tell much more than that... 

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EDIT2: Disabled NoScript completely, uninstalled the NoScript version, reinstalled the regular version (with Firefox restarts inbetween) - and the behavior is the same as listed above: the toolbar button appears, but the iframe is not populated.

So the NoScript.user.js version indeed solves the NoScript problem - but it seems the empty iframe problem is due to Firefox or Greasemonkey specifics, and not due to NoScript blocking.

  [1]: https://i.sstatic.net/qnRL4.png