One known problem with firefox is a setting for the maximum connections, that sometimes caused Windows machines to freeze on Firefox 7. There is a workaround, but it is Fixed in Firefox 8 which is released Today.

• see http://blog.bonardo.net/2011/09/30/is-your-firefor-freezing-at-regular-intervals

Problems with speed at certain times of the day may often be related to internet speed at a particular time of day, or how busy a particular site is.

You may get suggested solutions on this site, but you will not be likely to the get attention of any developers.

Thank you John99. Your answer helped, just a shame I had to actually use Google Chrome to download Firefox Version 8 as the previous version was still 'hanging' from 7am this morning, 12 hours ago!

Glad it seems to be working again now.

Firefox does have faults, and these hangs that were missed is one example.

My understanding is that developers are now working on automated tests that will report hangs, in much the same way that there are automated reports generated when firefox crashes. And are trying to get hang duration added to the data users can send as part of the telemetry monitoring option.