I recently updated to Firefox 18.0.1 on my Macbook Pro, and I have noticed a few issues;
1) Google Maps won't function, I can load up a map, but is stays with a 'Loading...' and then 'Still loading... Slow? Use the troubleshooting guide or basic HTML.' message. I have performed the steps provided in troubleshooting to no avail
2) Problem viewing thumbnail videos on the right hand side bar of YouTube. Usually I am able to see the video thumbnails, but I have noticed it now does not show an image at all
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.