[ENHANCEMENT] Group desktop/mobile browser updates in notification emails

[rviscomi]

In today's notification email, there were 5 features that became available in Firefox, but 10 entries under the "Browser support changed" section:

There were separate entries for desktop and mobile browser versions. This makes it harder to skim the list to understand what changed.

I would expect to see one "Firefox" entry per feature, like this:

Otherwise, for example if there was a change ONLY to the Android version and not the desktop version, I would definitely expect to see an entry for "Firefox Android".