Align placeholder better

[shuhaowu]

The placeholder needs to be aligned better, especially the inline one as the inline one is a little bit off.

Furthermore, sometimes there are incorrect detection:

• en-US/kb/customize-navigation-buttons-back-home-bookmarks
• en-US/kb/sort-bookmarks-quickly-find-ones-you-want (with Mac)

[shuhaowu]

I don't think there is a way to be completely reliable in the way that we detect inline vs blocks.. Mostly when we mix in showfor it gets wrong frequently.

However, since the target is Firefox OS I don't think this is a big big deal

Moved to nice to have.