In Bug 1743914, we made it easy to collect whether Firefox is the default PDF handler. This ticket tracks doing the same for the mailto protocol.

While here, perhaps we can also include whether Firefox itself has a registered mailto protocol handler, so that launching Firefox to handle mailto actually does something helpful.

If we can include a single extra bit, it would be helpful to also include if the default handler is a non-Firefox known-browser, i.e., Edge, Chrome, Brave, etc.

While here, perhaps we can also include whether Firefox itself has a registered mailto protocol handler, so that launching Firefox to handle mailto actually does something helpful.

gijs: is this already instrumented? I see nothing immediate in probes.telemetry.mozilla.org but this is absolutely not my domain.

(In reply to Nick Alexander :nalexander [he/him] from comment #1)

While here, perhaps we can also include whether Firefox itself has a registered mailto protocol handler, so that launching Firefox to handle mailto actually does something helpful.

gijs: is this already instrumented? I see nothing immediate in probes.telemetry.mozilla.org but this is absolutely not my domain.

I don't believe so. There's no generic telemetry about what apps are used for what filetypes / protocols because doing so in a way that is privacy-preserving would take work (executable paths and handler URLs can contain PII, and I suppose potentially even file extensions or protocols could be used in identifying ways in some circumstances). It should be fine to do it specifically for mailto and for whether it is set to a specific handler or not, but I don't think we have that today, from looking at e.g. https://searchfox.org/mozilla-central/source/uriloader/exthandler/ExtHandlerService.sys.mjs which would be the natural place to add some of that telemetry.

(In reply to :Gijs (he/him) from comment #2)

(In reply to Nick Alexander :nalexander [he/him] from comment #1)

While here, perhaps we can also include whether Firefox itself has a registered mailto protocol handler, so that launching Firefox to handle mailto actually does something helpful.

gijs: is this already instrumented? I see nothing immediate in probes.telemetry.mozilla.org but this is absolutely not my domain.

I don't believe so. There's no generic telemetry about what apps are used for what filetypes / protocols because doing so in a way that is privacy-preserving would take work (executable paths and handler URLs can contain PII, and I suppose potentially even file extensions or protocols could be used in identifying ways in some circumstances). It should be fine to do it specifically for mailto and for whether it is set to a specific handler or not, but I don't think we have that today, from looking at e.g. https://searchfox.org/mozilla-central/source/uriloader/exthandler/ExtHandlerService.sys.mjs which would be the natural place to add some of that telemetry.

I understand that the details are sensitive, but the existence of a registered handler is not. Sounds like we don't collect that; this ticket will track doing so.

I think what we want to know is determined here: https://searchfox.org/mozilla-central/rev/55d8d8e0e00ab140088122be39f05e4cd867616a/browser/base/content/nsContextMenu.js#330-338. I'd lift that into nsIHandlerInfo and include it in telemetry around https://searchfox.org/mozilla-central/rev/132ffbfd6842e5ecd3813673c24da849d3c9acf8/browser/components/BrowserGlue.sys.mjs#2663.

It's not 100% clear to me how to answer my second question, about whether the default handler is a non-Firefox browser. It appears that mailto: is a protocol like any other (i.e., https) and is protected by UserChoice, so maybe our existing .pdf telemetry collection, just works out of the box? That would be pleasant.

(In reply to Nick Alexander :nalexander [he/him] (PTO until Montreallhands August 21, 2023) from comment #4)

I think what we want to know is determined here: https://searchfox.org/mozilla-central/rev/55d8d8e0e00ab140088122be39f05e4cd867616a/browser/base/content/nsContextMenu.js#330-338. I'd lift that into nsIHandlerInfo and include it in telemetry around https://searchfox.org/mozilla-central/rev/132ffbfd6842e5ecd3813673c24da849d3c9acf8/browser/components/BrowserGlue.sys.mjs#2663.

So to be clear, that checks whether Firefox itself would handle mailto links it encounters on webpages using a web app (like gmail or similar).

It's orthogonal to whether the OS thinks that Firefox is the default handler for mailto apps outside of Firefox. You would need different code for that. Specifically, you can use something like this:

https://searchfox.org/mozilla-central/rev/8f09f6a6ff0d8b6ea75a1e1279a06ba02479578c/uriloader/exthandler/nsMIMEInfoImpl.cpp#367-378

It should also be possible to call this from JS. The implementation already has the full path (but doesn't expose this), and you could probably use that to identify Chrome/Edge as needed.

It's not 100% clear to me how to answer my second question, about whether the default handler is a non-Firefox browser. It appears that mailto: is a protocol like any other (i.e., https) and is protected by UserChoice, so maybe our existing .pdf telemetry collection, just works out of the box? That would be pleasant.

Last I checked the way Windows deals with protocols vs. files was subtly different, so I'm not sure this would be the same, but see my previous response.