The details tag currently (March 2016) works in Chrome (and Opera, Safari) and is expected in Firefox in v47 by June 2016. (Update: expected in Firefox v49 by mid-September.)
Here is an example (code first):
<details>
<summary>Some details (click to open/close)</summary>
<p>
Duo equidem mediocrem mnesarchum eu. Dicat fastidii suscipiantur cu
has. Viris alterum accumsan pro id, in verear delicatissimi pri. Cu quod
quas pri. Mei summo scaevola interesset no, et ignota animal vel.
...
</details>
Duo equidem mediocrem mnesarchum eu. Dicat fastidii suscipiantur cu has. Viris alterum accumsan pro id, in verear delicatissimi pri. Cu quod quas pri. Mei summo scaevola interesset no, et ignota animal vel.
Cum nihil quaerendum no. Usu ei scaevola concludaturque. Quando malorum scribentur ut vel. Mei id mucius virtute. Debet percipitur quo ad.
No has vide docendi commune. Mel ad alii zril verterem, vidit elaboraret consequuntur mel et. Ius diam melius deleniti te. Purto blandit vix ad, labitur officiis te vel.