Strange message: Firefox Android
The message there is a more recent version of the page on the server, do you want to reload? is shown by the web site itself. It is generated via JavaScript and other web techniques and therefore can vary by size, displayed text and other properties.
When you re-open Firefox the previously cached web page is displayed.
Some web sites use special web techniques (JavaScript + WebSocket) to connect to the server in background and check for provided update information.
For example the Stackoverflow/Stackexchange web pages also use this technique for displaying an info header that new questions are available or that there is a new message in your &quot;inbox&quot;.

Therefore if your browser first loads the cached page and then checks for updates and displays this message. As the message is generated by the web page, not by the web browser itself it will only appear on web pages that use this technique and it may look totally different on each page.