Fix bug 867810 - update /features page content

* Changed "Personas" to "Themes"
* Changed "App Tabs" to "Pinned Tabs"
* Updated SuMo link for pinned tabs
Small fixes for firefox/partners animations. Bug 866756.
Merge pull request #852 from jpetto/bug-866756-partners-animations

Small fixes for firefox/partners animations. Bug 866756.
Merge pull request #856 from craigcook/bug-867810-update-features-page

Fix bug 867810 - update /features page content
Update suggestions.txt
Merge pull request #862 from dad7732/patch-4

Update suggestions.txt
Bug 867916 - Add promo-images as background-images instead on img elements