In the Debugger in Firefox Developer Edition I've set a breakpoint to land on the assignment to a JavaScript variable. I expected to be able to hover over all previously defined variables to view their values within a tooltip like in previous versions of Firefox, but it doesn't show me anything and there doesn't seem to be a window I can add to the side:
Any ideas how to display the variable values?
As described in an answer to a similar question, the Debugger panel in the Firefox Developer Edition 52.0a2 was actually an external project reworked from scratch, which didn't have all features of the original Debugger panel at that point in time.
This feature was not implemented in that version yet.
In that version, you had to look at the side panel under Scopes to see the variable value.
In newer versions of Firefox, this feature is available by default. Though back then you could have switched to the old UI by setting the preference devtools.debugger.new-debugger-frontend in about:config to false to get that feature back.