[CRX] Fall back to sender.tab.url if !tab.url

sender.url is relatively new (Chromium 29)
 ( https://chromiumcodereview.appspot.com/14301016 )
[CRX] Remove redundant location.origin check

The PDF Viewer will always be rendered directly from the extension,
so checking "origin == chrome-extension:/.." is not needed any more.
( since edd4bae903c36048b7d4d4bed393e4408d0198ba )
Register as File browser handler in Chrome OS
Remove obsolete code from shortcut handler

These lines were introduced in 612f59aa10eef2bf6559deddfb54b84a0a30c6bc
when the only shortcuts were +/-/=/0 (to change zoom level).
Back then, when the input fields were focused, using these keys would
add these unwanted characters to the input field and change the zoom
level of the viewer. Having both operations at the same time was an
undesired event, so a check was inserted, to ignore shortcuts when
the toolbar is focused.

The #toolbar element doesn't exist any more, so these lines are obsolete.
[CRX] Pass expected length of stream to viewer

To get a progress bar for POST/FTP requests in Chromium.
Handle navigation keys when viewer is not focused

Restrict the scrollbar hack to the keycode for "spacebar",
since the bug only occurs in Firefox with spacebar.

Keyboard navigation is only activated for the spacebar if
the currently focused element is not a button.
Backport latest zh-TW strings from l10n-aurora
Merge pull request #4256 from moztw/0207_zhtw

Backport latest zh-TW strings from l10n-aurora
Do not switch to a range request for small PDFs
Merge pull request #4258 from Rob--W/network-reduce-requests

Do not switch to a range request for small PDFs
Removes -moz-box-sizing usage
Change test font to one that works with ttx v2.4.
Merge pull request #4272 from brendandahl/change-test-font

Change test font to one that works with ttx v2.4.
Update ja locale
Merge #4274
Merge pull request #4191 from Rob--W/crx-chrome-os

Register PDF Viewer as PDF handler in Chrome OS's file browser
Fix wrong page being displayed when entering/exiting Presentation mode with zoom set to 'page-fit'
Bug 972435 - Recompress all PNG assets
Merge pull request #4287 from gabrielesvelto/bug-972435-recompress-png

Bug 972435 - Recompress all PNG assets
Update cs locale