@vB9 no idea tbh. could be something with firefox? i dont use it personally but i know it sometimes has trouble with some features/functions. didnt change anything about the embeds and i've never had trouble with them
and right now my plan for the themes is to have two categories: old school ones with the old forum's "vibe" and a different modern looking one (DarkThemeV2)
right now i think im pretty much done with "darker red w white text", this is the one i've set as the default theme for the time being
when i have the time i plan on creating a couple of new widget pages and fixing some colors and sizes for the other old timey themes (like the OG Red and the light theme ones) and then polishing the modern DarkThemeV2 one that i think will become the default theme after im done it (with the idea that a modern looking page will be attractive to new users, old members can still go for the nostalgia look and use darker red or other vBulletin inspired variants)
added
@brk 's logo to the DarkModeV2. looks great and IMO fits that Theme better. new era new personality. but the old school looking ones i want keep as intact as possible, i will keep using the same fonts and images as the old RNB and will try remain as close as possible to the old color palette