software details:
manifestVersion: 1.2.5
cookieEnabled: true
doNotTrack: unspecified
language: lt
buildID: 20200309095159
name: Firefox
vendor: Mozilla
version: 74.0
arch: x86-64
os: linux
Most Iridium features are broken since this morning, possibly an update on YouTube made it unusable, as auto-play can not be disabled, also no controls in page whatsoever. Screenshots:

Iridium just installed in new fresh profile, with icon missing in page.

No quick controls below player too :\
steps to recreate the problem:
additional information that could be helpful:
Ubuntu Linux 18.04 LTS, Xfce desktop.
I can see the same thing on my end, YouTube changed something, will see what is going on.
Initial assessment confirms changes on YouTube side. A script name was changed from:
desktop_polymer_sel_auto_svg_home_v2.js
to
desktop_polymer_inlined_html_polymer_flags_v2.js
Simply adding that new URL in https://github.com/ParticleCore/Iridium/blob/master/src/js/background.js#L503-L509 will make the remaining features work again, with the exception of the missing UI elements which I am still checking.
Along with the previously mentioned change, the contents of the UI elements have also migrated, this time into an inline in the previous script. The fix is to adjust the injection point of these elements for them to be displayed correctly.
Most helpful comment
Along with the previously mentioned change, the contents of the UI elements have also migrated, this time into an inline in the previous script. The fix is to adjust the injection point of these elements for them to be displayed correctly.