When the user selects "Remove All Breakpoints" it should wipe all of the save breakpoints. This will make it easy for users to stop seeing phantom breakpoints.

 export function removeAllBreakpoints(cx: Context) {
   return async ({ dispatch, getState }: ThunkArgs) => {
     const breakpointList = getBreakpointsList(getState());
-    return Promise.all(
+    await Promise.all(
       breakpointList.map(bp => dispatch(removeBreakpoint(cx, bp)))
     );
+
+    // I think we should also clear all the pending breakpoints as well.
   };

I would like to try tackle this.
Would something like this work?

const breakpointList = getBreakpointsList(getState()).concat(getPendingBreakpointList(getState()));
    return Promise.all(
      breakpointList.map(bp => dispatch(removeBreakpoint(cx, bp)))
    );

hmm, i'm not sure what the best way to clear the pending breakpoint list. but either way, it is yours :)

Add action for clearing pending breakpoints

https://hg.mozilla.org/mozilla-central/rev/1d506ae7fd6b