Some sites that have worked well in previous Firefox version 44.0.2 when third-party cookies were blocked, have stopped loading when ‘Accept third-party cookies’ setting in Privacy preferences of Firefox 45 was set to “Never’.

For instance, one such affected site inbox. Google.com has refused to load, and displayed the error: ‘ Server is temporarily unavailable’, and then on tries to refresh the page itself in a never-ending loop. After reported by affected users, Mozilla has acknowledged the issue and fixed it with .dot release, Firefox 45.0.1. 

Firefox privacy preferences

Apart from this, this small update also disabled the graphite font Shaping library due to security issues. There are other bugs fixed as well with this release, check Firefox 45.0.1 release notes for more details.