Related to #3071

Meta-issue to address #3071.

We now know that storage is overflowing for some users, and this may be causing vault loss.

We need to develop strategies to improve our storage size resilience, and implement them.

• Study what happens when background localstorage cannot write anymore. Is the storage instantly lost? Is there an opportunity to backup/recover?
• Study which portions of our persisted state take the most size (probably transactions).
• Review extension storage limits.
• Research other alternative storage strategies.
• Move our localStorage use to the better solution (storage.local).