Yeah, I switched to Firefox when this whole Manifest V3 thing was announced, I only still have Chrome installed because it's better for PDFs than Firefox and once in a great while i run into a site that doesn't work right on Firefox.
I actually really like Firefox for reading pdf's, how is it in chrome? I've never actually tried chrome for that because I was still using okular back when I still had chrome installed on anything.
The main issue I have with Firefox is that some pdfs have this side-by-side layout (especially rpg pdfs) that Firefox respects and I keep having to turn it off every time I load a new one. Chrome doesn't respect it and shows it a page at a time like I want. My eyes don't work too good so side by side the text is just too small.
Interesting, funny enough I have sorta the opposite problem using Firefox for PDFs: I like the side by side view of two pages and Firefox always loads books with single pages, zoomed way too far in for my taste. Have you tried it for PDFs recently? It's a new way of reading them for me, and I wonder if they've changed it since you used it last.