I have also been experiencing frequent tab crashes in Firefox when using Quickbooks online.  Although the incognito solution works, it is very inconvenient to my work flow.  Crashing usually happens when working in a new invoice or purchase order.  After clearing the cache the problem does not resolve in a regular browser.  This never happened prior to the most recent changes. 

I have found that crashes seem to be prevented if you SAVE after you enter in the first item on an invoice or a PO, but that is just another step I shouldn't have to take. 

Quickbooks, please fix this!