Product Firefox Release Channel release Version 51.0.1 Build ID 20170125094131 OS Windows 7 OS Version 6.1.7601 Service Pack 1

Signature: mozilla::net::nsStandardURL::EqualsInternal

This is for Sumo's Related Bugs 1313085 NEW --- Crash in mozilla::net::nsStandardURL::EqualsInternal [Websense]

Update Websense. if there is still a problem, disable it.

if you mean this Websense -https://www.forcepoint.com/product/web-filtering/websense-web-filter-security then it's a corporate software and i don't have any access to it...

unfortunately this crash is caused by the websense/forcepoint security software that is running on your device. in a corporate environment, please get in contact with your it department to make sure that websense is fully up to date, as it has the tendency to crash newly released firefox versions until they adapt accordingly.

another option would be to install an esr version of firefox: Old versions of Websense cause startup crashes in Firefox