Hey Shirley - The only subscription where Cross Browser Testing is not available is the bronze package. Otherwise, this should be available. https://www.optimizely.com/pricing.
However, there is a recent product update that gives you additional options for the project settings of the snippet. This update gives you increased control over what's included in the snippet. One of settings was turned on by default to prevent third parties from linking to your variation without your knowledge. The downside to this is that you will not be able to use the cross browser testing functionality or be able to "force a variation" to display using query string parameters.
If you want to enable this setting again to use Cross Browser testing, simple click "Project Settigs" from your dashboard, "Project Code Settings", and uncheck the box under "Force Variations". See the attached screenshot for reference. If you want, you can always enable this feature during QA and then disable it again once you have set your experiment live.
Let me know if you have any questions on this, or if there is anything else that I can help you with.