v5.x backports tracker ticket

[totaam]

Issues that we may want to apply to the old v5.x branch if there is enough demand:

• multiple sessions behind reverse proxy: b944a32f4b3a1394e092095e6ab57d575b764307
• increase max video size: 69c4e7d36ba1dca420f7b4e07224133b20298489
• URL parameters (risky - caused regressions): 864dc00808c6caab238578919cc2442488d4c9cf, c07629f9383dafffbcd146747ffc647c50f4c336, 7f3aa77e69eb4822d40490dc31f21f2fcbee9816, 81692ba11c34da0968e9c8f72119f7831b944b62
• download bug? 0ce0a70bdaf383e539d0e90fb701c241dc91c1dd
• clipboard can be enabled? 6657db765d01a13a097f32e0313e3ad3c571f4c8, 5271a4fbaf316b45463985bceb6e9e152eb6c568