Playlists, reworked:
• Click a playlist to play it; open it for per-track actions, Play and Shuffle
• Long playlists now load instantly and page in as you scroll
• Save the currently playing song into any playlist in two clicks, with an "already added" guard
• Remove songs from your playlists, with a confirm step

New actions menu:
• The ⋯ menu is now a bottom sheet with everything visible at once
• Sleep timer presets inline, plus a live countdown on the album art while a timer runs

Player:
• Hover the seek bar to preview the exact time before you click
• Tracks over an hour show the correct time (5:01:39, not 301:39)
• The popup stays usable when YouTube Music is open with nothing playing - search, playlists and history work, so you can start the music from here

Fixes:
• Queueing the same song twice no longer mixes up artwork between the copies
• "Play next" inserts after the song that's actually playing
• More reliable lyrics matching for multi-artist tracks; a lyrics-service outage is no longer remembered as "no lyrics"
• Refreshed icons, consistent spacing, and a dozen smaller fixes

Note: versions 1.0.1-1.0.3 were store-listing housekeeping only - this release brings Firefox fully up to date.