Update 6.2 release requirements for Volto and Classic UI (#2030)

Author: stevepiercy

docs/_inc/_install-browser-reqs-classic-ui.md

@@ -1,7 +1,7 @@
 You can view the list of supported browsers for Classic UI at [Browserslist](https://browsersl.ist/#q=%3E%3D+0.5%25%0Alast+2+major+versions%0Anot+dead%0AChrome+%3E%3D+60%0AFirefox+%3E%3D+60%0AFirefox+ESR%0AiOS+%3E%3D+12%0ASafari+%3E%3D+12%0Anot+Explorer+%3C%3D+11).
 
 The supported web browsers for Classic UI are set according to [Bootstrap](https://getbootstrap.com/docs/5.3/getting-started/browsers-devices/#supported-browsers).
-The following code snippet is the [browserslist configuration for Bootstrap 5.3.3](https://github.com/twbs/bootstrap/blob/v5.3.3/.browserslistrc).
+The following code snippet is the [browserslist configuration for Bootstrap 5.3.8](https://github.com/twbs/bootstrap/blob/v5.3.8/.browserslistrc).
 
 ```shell
 >= 0.5%
@@ -13,4 +13,5 @@ Firefox ESR
 iOS >= 12
 Safari >= 12
 not Explorer <= 11
+not kaios <= 2.5 # fix floating label issues in Firefox (see https://github.com/postcss/autoprefixer/issues/1533)
 ```