Reduce disk activity by disabling some unnecessary tasks and telemetry

Activity stream needs to be disabled again. Telemetry tasks that cause disk activity should ideally be conditional. toolkit.telemetry.enabled is true on nightly builds, that should be locked to false to keep it consistent across all builds. webextensions.storage.sync.enabled could be set to false to eliminate 3 files from the profile folder. These will reduce the noise while monitoring files and preferences and could improve the stability and performance of the browser.

bd5c511f disables LaterRun which stores the profile creation time in browser.laterrun.bookkeeping.profileCreationTime and the number of times the browser has been opened since then in browser.laterrun.bookkeeping.sessionCount.