Extension Blocklisting:New Attribute Crashes Since Last Request

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Currently we use requests for extension blocklists to determine "Active Daily Users" ADU. This isn't an accurate name as ADU actually is just active installs.


We are working on pulling ADU into http://crash-stats.mozilla.com in order to give context to our crash trend reports.

Our current "total crashes" numbers are a shaky baseline for the following reasons

  • users may opt-out of submitting a crash and we have no way of knowing the opt-out rate
  • crashes are throttled so ADU to number of crashes have to be adjusted on a product/version basis

By piggybacking on ADU we eliminate these opt out issues. ADU on the other hand is also opt out. The reasoning behind this number being more trustworthy is

  • ease of opting out during a crash reporter versus blocklist opt out
  • stress of "just wanting to restart"
  • change of opt-in versus opt-out skewing this rate across prod/version

Proposed Change

If we added a new attribute to the blocklist request *Crashes Since Last Request* then we would have a more accurate baseline for looking at crash velocity and severity.

Work Required



The #1 priority is user privacy and this does not trump our commitment to code quality.

It seems like this change would be compatible with the spirit of our current privacy policy, but that an update needs to be made to "Blocklist Feature" section where it lists the exact information sent.

The basic Privacy issues on this are:

In the past the protocol was for the browser to request a block list and the service would return the blocklist.

With this change the protocal would be for the browser to request the blocklist *and* to also include an indication of the number of crashes since the last blocklist request. the service would return the block list as it previously.

Current Policy

Blocklist Feature

Firefox 3.x also offers a Blocklist feature. With this feature, once a day Firefox does a regularly scheduled, automatic check to see if you have any harmful add-ons or plug-ins installed. If so, this feature disables add-ons or plug-ins that Mozilla has determined contain known vulnerabilities or major user facing issues or fatal bugs (e.g., client crashes on startup or something causing an endless loop of unusability). You may view the current list of Blocklisted items. This feature sends Non-Personal Information to Mozilla, including the version of Firefox you are using, operating system version, build ID and target, update channel, and your language preference. In addition, Mozilla also uses this feature to count the number of active Firefox users. Currently there is no basic user interface to disable the Blocklist feature. An article in our Firefox Knowledge Base explains how you may disable the Blocklist feature. Disabling the Blocklist feature is not recommended as it may result in using extensions know to be untrustworthy. More information about the Blocklist feature may be found at https://wiki.mozilla.org/Extension_Blocklisting.

Adjusted Policy

Change the wording of above to indicate the transmission of "number of crashes" as one of the items reported. And to reflect this data will be used to measure the effect of changes made by Mozilla and third parties such as Plugin and Addon vendors to improve stability.