Fixing detection of IE 11 masking as Firefox

[ibash]

I got the user agent from a IE11 on windows 7 vm from here: http://www.modern.ie/en-us/virtualization-tools
It was being detected as firefox, this corrects that.

[bnjmnt4n]

Did you test the latest platform.js?

[ibash]

Yes, this was me testing against master (commit 0d310f8).

[bnjmnt4n]

As far as I know, the IE11 user agent does not include Firefox. @jdalton can you confirm this? Are you sure you’re not using an extension?

[jdalton]

As far as I know, the IE11 user agent does not include Firefox

@ibash Is talking about masking as Firefox via F12 emulation options which allow running canned UA strings, one of which is Firefox.

[ibash]

@D10 / @jdalton When I grabbed that user agent I didn't think IE was emulating firefox, it looks like it is though as the default user agent is: Mozilla/5.0 (Windows NT 6.1; Trident/7.0; rv:11.0) like Gecko

You can close this if you don't want to support it, otherwise I can expand this to support all user agents of IE11 emulating other browsers.

[bnjmnt4n]

Apparently this has something to do with compatibility mode, which was extended in IE10+ to allow site specific user agents, including user agents of other browsers. I will have to think through how to deal with this.

[bnjmnt4n]

I've added support for detecting IE identifying as other browsers, but not IE masking as other browsers yet. @jdalton do you think we should do that? We could probably just use document.documentMode to find out if the browser is IE, though I'm not sure if other browsers also have document.documentMode.

[ibash]

@D10 Side note -- for our needs that changes you have made (bumping platform.js version and IE commit) are plenty. Not sure what use cases there are for detecting masking, or correct behavior is there.

Thanks for fixing this!