Do not enable object resizing in gecko

Description of this can be found [here](https://developer.mozilla.org/en-US/docs/Web/API/document.execCommand). Here is a screenshot of what this does:
![screenshot from 2014-12-17 22 01 25](https://cloud.githubusercontent.com/assets/635591/5477914/4560fb14-8638-11e4-8c7f-f3e86965b74e.png)
The attributes do indeed pass through the parser.

Do we want this? Other browsers don't have this feature, or have it turned off. I just checked and Chrome doesn't seem to have this.

I can see how this can be useful with images in some cases, but this really should be the role of module specific for this purpose, with tests and consistent cross–browser behavior.

If we turn this off now, will some users be upset?

With tables it can make a mess of the table, in an unrecoverable way. Here is what I managed to do:
![screenshot from 2014-12-17 22 15 15](https://cloud.githubusercontent.com/assets/635591/5478127/4ca172ee-863a-11e4-80a1-7e02e4980239.png)

So I think this should be removed, with an appropriate message in the changelog.