Bug 844219 - installing again an uninstalled app is not displaying correctly the size r=etienne

- use updateManifest.size if there is an updateManifest, use manifest for the
  other properties if manifest is present
(cherry picked from commit 7f0a1d5341ac8870e70f64f543ec79a729bf717e)
Merge pull request #8210 from lodr/bug-841439-system-dialogs

Bug 841439 - Custom select dialogs replaced by standard <selects> and custom warnings removed in favor of system alerts
Cause r+(cherry picked from commit 8b955ec03bb86187e2a21c5d24c0ff06e35324cb)
Bug 842500 - "TypeError: Floating-point value is not finite." when assigning undefined to a <progress> value r=etienne

- use removeAttribute instead of assigning undefined
(cherry picked from commit 95d47f725af83e701aefa694d1a90ae7fe8a5d95)