Bizarre issue with LibreWolf

So, I’ve switched over to LibreWolf for my daily browsing. Everything seems pretty smooth for the most part, but I hit this weird snag on some old message boards—specifically when I stumble onto a thread with embedded YouTube videos. Instead of just playing, my browser starts throwing these endless pop-up windows at me, asking if I want to save a file with an .swf extension. It’s like a relentless barrage... five, six prompts in a row, and I just have to sit there clicking "cancel" over and over again. I haven't actually counted them, but it feels like it's triggered by every single embedded video on the page. I'm well aware this isn't a bug with the site itself, but rather something funky going on within my own browser settings. I was hoping maybe someone here has run into this exact headache before and figured out a fix...
Thanks.