Bug 857901: Increase keyboard character-delete speed

UX informs me that 75ms seems to be a good interval, and that the
initial delay is fine where it is.
Bug 875248 - New unit tests for wallpaper.js
Bug 877960: followup to check the pref by default.
Merge remote-tracking branch 'upstream/master'
merge
Merge remote-tracking branch 'upstream/master'
Merge remote-tracking branch 'upstream/master'
Merge remote-tracking branch 'upstream/master'
Merge remote-tracking branch 'upstream/master'
Merge remote-tracking branch 'upstream/master'
Bug 877990 - Adding minimum delay between automatic requests to respect performance limits
Merge pull request #10166 from lodr/bug-877990-performance-limits

Bug 877990 - Adding minimum delay between automatic requests to respect performance limits.
r=@jmcanterafonseca
Merge pull request #10035 from crdlc/bug-875248

Bug 875248 - New unit tests for wallpaper.js
Bug 879177 - Can't fully scroll when searching (first time) contacts
Revert "Merge pull request #10166 from lodr/bug-877990-performance-limits"

This reverts commit 742caa314f950159603a92e08b423b76486f7ffe, reversing
changes made to f9318db4067b23842b3ac16bc2956a6e3c38e306.
Bug 877990 - Adding minimum delay between automatic requests to respect performance limits.
Merge pull request #10186 from lodr/bug-877990-performance-limits

Bug 877990 - Adding minimum delay between automatic requests to respect performance limits.
r=@jmcanterafonseca
Bug 877615 - [MMS] New message composer: Recipients field stays expanded after discarding a previous multi recipient message - r=gnarf37

- #messages-recipients-list is declared "singleline" in markup
- Test to enforce recipient list always begins in singleline mode

Signed-off-by: Rick Waldron <waldron.rick@gmail.com>

Closes gh-10193
Bug 875690 - [MMS] [UX] Thread view. Wrong alignment of elements - r=gnarf

Closes gh-10091
Merge remote-tracking branch 'upstream/master'