In Firefox (Android), when you have a tab already opened and you switch to another, when you return to the previous one you will see that Firefox reloads the tab again, which is the case on every tab. See how you can easily disable this feature.
The reason this happens is because of the operating system, where it stops any function that is not active at the moment, in order to save memory for the system. Do not try the following mode if your phone does not have enough memory (over 2GB).
Open a new tab and type as URL:
about:config
It will show you some options of Firefox. Click on the Add button (Cross).
In the field that will appear, type:
accessibility.blockautorefresh
Now select "Boolean" on the right and "True" at the bottom. Now save the new setting and exit the menu. You will see that when you change tabs it will not reload them.
To disable this feature, go back to the Settings Menu, select the setting you just added and change the "True" to "False".