My scrollwheel isn't working on some pages, yet pages in other tabs scroll just fine. It's not a focus issue.
It's weird—for the past few days my Firefox has been very erratic in acknowledging the use of my scrollwheel. Some pages work just fine. Other pages refuse to scroll at all, or only scroll if I have my mouse cursor positioned in some (seemingly random) spot.
I experienced a similar problem when I had the buggy Facebook Messenger windows app installed, and killing that seemed to fix my troubles. Now, I can't place the blame on any background apps like that, and I've just restarted, and I haven't installed any new addons, either.
Re: My scrollwheel isn't working on some pages, yet pages in other tabs scroll just fine. It's not a focus issue.
If a plugin or other scrollable area has focus then you may not a able to scroll.
Can you post a link?
Start Firefox in Safe Mode to check if one of the extensions (Firefox/Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance).
Do NOT click the Reset button on the Safe Mode start window or otherwise make changes.