Last Friday, we discussed this bug.
Our primary objective behind suspensible/restartable background contexts (event pages / service workers) is to have extensions that are resilient against sudden termination. This is needed on Android, and to a lesser extent on desktop.
In Firefox's current implementation, the lifetime can easily be extended indefinitely (bug 1748533), which may interfere with the goal of having extensions that are resilient by design. I'm not against supporting extensions that really have these needs, but would like that to be more explicit, rather than through some wasteful work-arounds. For example, having stricter lifetime limits by default, plus an opt-in advisory entry in the manifest file (e.g. a permission as suggested at https://github.com/w3c/webextensions/issues/44).
Luca suggested to evaluate the possibility of moving the event page to the bfcache (instead of a full shutdown) to reduce the initialization overhead of event pages. While that doesn't help against sudden termination, it could reduce the cost/overhead of suspending/resuming event pages.
The next step here is for Luca to draft a document about the background's lifecycle / lifetime from where we can continue the discussion.