Fix bookmarklet on mobile browsers, eg Firefox

[snarfed]

First off, thanks for maintaining Press This, it's great!

The bookmarklets stopped working for me in Firefox Mobile a while back; background in mozilla-mobile/fenix#2871 (comment). Turns out opening a new window was the culprit. I fixed it for myself by removing lines 149 (target) and 152 (window.open) here so that it opens in the current window instead:

press-this/assets/bookmarklet.js

Lines 149 to 152 in 9ca88fa

	form.setAttribute( 'target', target );
	form.setAttribute( 'style', 'display: none;' );
	window.open( 'about:blank', target, 'location,resizable,scrollbars,width=' + windowWidth + ',height=' + windowHeight );

We could just maintain a separate copy for mobile browser, but obviously it'd be better to keep them unified. I don't know how to sniff for mobile browsers though. Do you? Any idea how you'd want to incorporate this?

Thanks in advance!