Update our browserslist config (twbs#30986)

Use browserslist defaults which is `> 0.5%, last 2 versions, Firefox ESR, not dead`

.browserslistrc

@@ -1,13 +1,14 @@
 # https://github.com/browserslist/browserslist#readme
 
->= 1%
-last 1 major version
+>= 0.5%
+last 2 major versions
 not dead
 Chrome >= 60
 Firefox >= 60
 # needed since Legacy Edge still has usage; 79 was the first Chromium Edge version
 # should be removed in the future when its usage drops or when it's moved to dead browsers
 not Edge < 79
+Firefox ESR
 iOS >= 10
 Safari >= 10
 Android >= 6