Bug 926852 - [Messages] Read receipts feature Gaia implementation
Bug 960215 - [B2G][Messages] Image-attachment does not fill the screen in landscape orientation
Bug 971565 - [System2] Instantiable Title

- update test
- update bootstrap.js
- add necessary mock for bootstrap_test.js
Merge pull request #15512 from huchengtw-moz/gallery/Bug_960215-gallery-open-activity-rotation

Bug 960215 - [B2G][Messages] Image-attachment does not fill the screen i..., r=djf
Merge pull request #16030 from steveck-chung/message-read-report

Bug 926852 - [Messages] Read receipts feature Gaia implementation. r=julienw , crh0716
Merge pull request #16358 from EragonJ/bug-971565

Bug 971565 - [System2] Instantiable Title
Bug 971452 - [System2] Instantiable ActivityWindowFactory