Strawberry Jellyfish

Easily create full screen image backgrounds and fading slideshows that stretch 
and adapt to the size of your page.
You can either use it as a global “cover” style background that will be 
displayed on all pages and posts of your WordPress website or you can give 
individual posts or pages including custom post types their own specific 
background – great for giving parts of a website a whole different look.
Jellyfish Backdrop makes fullscreen background slideshows easy by allowing 
you to assign multiple backgrounds to any page or post.
<ul>
<li>Unlimited number of post and slideshows.</li>
<li>Create different slideshows or backgrounds or different areas of your site.</li>
<li>Easy to use admin panels with sortable images and media library integration.</li>
<li>Display images in any page element allowing slideshows anywhere, not just as 
a background!</li>
</ul>
<h4>Demo</h4>
See the plugin homepage for demos and full details: 
http://strawberryjellyfish.com/wordpress-plugins/jellyfish-backdrop/
<h3>Usage</h3>
Visit the settings page to set up the global and default options. Here you’ll 
be able to set up a default background image that will be displayed on every 
page of your blog, enable or disable the global background or individual post 
and page background support as well as set up the default options.
To add a unique background image or slideshow to a specific post or page, 
first make sure that in the Enable Page and Post Type Slideshows section 
on the setting page, you check any post types you want to allow slideshows 
to appear on. You’ll now find a new area on the post / page edit screens 
where you can add images to the Backdrop Slideshow and alter fade time, 
slide display time and where the images will appear. Jellyfish Backdrop uses 
the WordPress image uploader and Media Library, so it’s easy to choose the 
images you want to use. You can also reorder the images by dragging. 
Once you’ve finished adding and arranging your images, be sure to save the 
post or your changes will not be saved.
Page / Post backgrounds will override the default background so it’s possible 
to define one background to be used site wide and another on a specific page.
By default images are shown as the main page background (body), however you 
can make the images appear as backgrounds to other areas of the page by 
supplying any valid element id or class name in the Container field on the 
admin page. eg. #main, .header

Jellyfish backdrop

Fullscreen background images and background slideshows on any WordPress post or page. Easily upload and select images using the media library.

Toni

This plugin enables you to display a Fullscreen Button on your site. The plugin can easy implement with a shortcode. 7 different Versions from the Fullscreen Button are current available.
<h3>Usage</h3>
Integrate the Shortcode in WordPress and you get the following Unicode Symobol ⛶ with the Full Screen Function. Full customize, for changing the size or color. The ⛶ Unicode Symbol works with the standard HTML text formats.
Update: Now with Support for Font Awesome. With a special Shortcode you get the Font Awesome Expand Icon for Fullscreen Mode.
Shortcodes:
Fullscreen Button (Unicode Symbol ⛶) [fullscreen_button] 
Fullscreen Button (Unicode Symbol 🡥) [fullscreen_button_2] 
Fullscreen Button (Unicode Symbol ↕) [fullscreen_button_3] 
Fullscreen Button (Font Awesome) [fullscreen_button_fa] 
Fullscreen Button (SVG Alternate) [fullscreen_button_a1] 
Fullscreen Button (Text Version) [fullscreen_button_text] 
Fullscreen Button (Switch Toggle) [fullscreen_toggle]

Fullscreen-Button

Fullscreen Button Plugin, with a stylable Unicode Symbol for your WordPress.

Jellyfish backdrop vs Fullscreen-Button