Hello D Smith,
Unfortunately, there is not a way currently to connect to an existing browser, but we are looking to support this in a future version of the framework.
I do not have the specifics on the connection methods for Firefox, but I checked tabbed browsing in Firefox out again.
It still looks like you will get an error when launching the in a new tab instead of a window. So you would have to use a new window when testing in Firefox.
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