(bug 39793) #simpleSearch placeholder styles for Firefox, IE

(bug 39793) #simpleSearch placeholder styles for Firefox, IE

Since some time ago Firefox and IE 10 also support styling for input
placeholders. (Opera supports placeholders themselves, but not (yet)
styling them.)

Firefox also applies regular input styles to placeholders, which is at
best weird, so we need to style the placeholder for it to display
reasonably (grayed out). (bug 39793)

Note the single colon for IE and Firefox and double one for Webkit:
these are pseudoclasses, not pseudoelements.

In Opera, the placeholder is always grey; #808080 on my system, but it
might differ on various setups. It's close enough to #999999 for us not to
care.

Further reading:
* http://stackoverflow.com/questions/2610497/change-an-inputs-html5-placeholder-color-with-css/2610741#2610741

Change-Id: I902abe16ac0cb7a55fe0d9ee7a2eec9a4e5a371a