Handle case where firefoxGcIntervals could be set to null (#6826)

packages/driver/src/util/firefox_forced_gc.ts

@@ -1,4 +1,4 @@
-import { get, isNumber } from 'lodash'
+import { get, isNumber, isNull } from 'lodash'
 
 export function createIntervalGetter (config) {
   return () => {
@@ -8,7 +8,7 @@ export function createIntervalGetter (config) {
 
     const intervals = config('firefoxGcInterval')
 
-    if (isNumber(intervals)) {
+    if (isNumber(intervals) || isNull(intervals)) {
       return intervals
     }
 

packages/driver/test/cypress/integration/util/firefox_forced_gc_spec.ts

@@ -27,6 +27,15 @@ describe('driver/src/util/firefox_forced_gc', () => {
       })).to.eq(99)
     })
 
+    it('returns null if firefoxGcInterval is null', () => {
+      expect(run({
+        browser: {
+          family: 'firefox',
+        },
+        firefoxGcInterval: null,
+      })).to.eq(null)
+    })
+
     it('returns the appropriate interval for open mode', () => {
       expect(run({
         browser: {