What data does Mozilla store from me?
Only what is in the sync server, or there is more?
Additional System Details
- Shockwave Flash 27.0 r0
- User Agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:55.0) Gecko/20100101 Firefox/55.0
The user chooses what data is synced in the sync menu. Is there a problem?
Normally, shortly after your initial installation, you get a prompt along the bottom of the browser window to make choices about some data sharing settings: Share data with Mozilla to help improve Firefox.
An obvious move, but still not clarifying...
Álvaro López de Quadros மூலமாக திருத்தப்பட்டது
I think there probably are statements specific to the Health Report and Crash Reporter as well as Telemetry.
Data you save using Sync is encrypted so Mozilla can't read that.
"What data does Mozilla store from me?" Sync shouldn't really be considered "storage". At best it is "transactional" or temporary storage to merge data from multiple devices to keep those devices Firefox user data "synchronized". One merged copy of the users data is maintained, with no backups of data from each device separately from the merged data.
IMO, Health Report data, Crash Reporter data as well as Telemetry data isn't really "user data". It is data about how well Firefox works for each user (or how it doesn't work for the user via the Crash Reporter) to help Mozilla spot problems with Firefox and to help them improve Firefox for the "greater good"; IOW, for all users as a group. The user can choose to not share that data with Mozilla by opting-out, but it is one-way with no communication back to the individual device.
And as jscher mentioned Sync data is encrypted when it is off each device; in-transit to & from the Sync server and while on the Sync server. A dual kA & kB encryption "key" is generated from the users Firefox Account password and those "keys" remain on each device in Firefox prefs; Mozilla never "see's" those dual "keys". If the user purposely or accidentally changes the Password for that Firefox Account the data on the Sync server is rendered useless; thus the users data is wiped from the Sync server for a "clean start". And that is where too many users have had problems due to Mozilla not explaining how Sync works completely enough, IMHO.
There is no real user control over Sync, beyond selecting from the 6 data categories - Tabs, Bookmarks, Passwords, History, Add-ons, & Preferences - that the user wants synchronized on or to each device. No "master" device, no "direction" control, and no way to make Sync a manual operation which was possible a few years ago before Sync for Tabs was added to Firefox. AND no way to for the user to access their data via the internet except thru a "connected" Firefox installation.
And IMO if the user makes massive changes to their Bookmarks (like re-organizing folders of bookmarks) and the user "pushes" the changes too fast there's a strong possibility that corruption may occur and then get sync'd to other devices. (On Windows I watch the Task Manager > CPU meter to see how hard Firefox is working to "digest" the changes to bookmarks when re-organizing - that can be a real shocker as to how hard Firefox is working to re-arrange the Places database.)
Note that you use the Firefox version from the Ubuntu repositories and this version may behave differently than the official release.