Running Windows 7 Pro x64, Intel core i7, 8GB RAM Firefox 40.0.3 was hanging a lot when browsing eBay pages after upgrading. Removing all addons did not resolve the issue, nor did clearing cache or re-installing 40.0.3. Re-installing 40.0.2 resolved the issue. Some change introduced in 40.0.3 or possible eBay site upgrade is causing one of the top ecommerce sites to becomes unusable. I recommend contacting ebay techs to resolve this issue if you believe the change did not occur on the Firefox end. Additionally, when bringing up the task manager application, I see the ffcert.exe is running most of the time when the hangs occur. I never noticed this app previously, but that may be due to the hang not occurring so I had no reason to keep task manager open.