Limiting deferrals doesn't sound too bad. 5 seconds might be a bit too short though. perhaps 10 ?
Bug 1841217 Comment 6 Edit History
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I guess that could work. We could even reuse this pref, https://searchfox.org/mozilla-central/search?q=page_load_deprioritization_period%28%29&path=&case=false®exp=false