How do I temporarily disable an app when there is no "Disable" option There are two memory hungry apps, Facebook and Facebook Messenger, which I want to disable at times but not always. I used:


settings &rarr; apps &rarr; downloaded &rarr; Facebook &rarr; force stop
settings &rarr; apps &rarr; running &rarr; Facebook &rarr; &lt;weird service name(s)&gt; &rarr; stop
settings &rarr; apps &rarr; all &rarr; Facebook &rarr; force stop


But the app restarts after few minutes, often accompanied by lots of thrashing. Ideally I would like to disable the app and remove it from memory until I decide to use it. What is the best possible solution?

Android version is 4.4.4, almost stock, not rooted.
Manual methods might be tricky here. I'd recommend taking a look at Greenify, which will take care for such apps automatically (after you've told it so – you're the boss after all ;)

 
Greenify (source: Google Play; click images for larger variants)

As the screenshots show, Greenify can "hibernate" apps automatically when the screen is off (and it can do the same when configured apps are not in foreground) – which is basically like an "automated freezing/disabling" of the app. Big difference: you no longer have to care for that yourself. App icons and everything remain accessible. From the app's description:


  Greenify help you identify and put the misbehaving apps into hibernation when you are not using them, to stop them from lagging your device and leeching the battery, in an unique way! They can do nothing without explicit launch by you or other apps, while still preserving full functionality when running in foreground, similar to iOS apps!


To point out some details which where misinterpreted1, please take a closer look at the first screenshot. You can see it shows 3 sections:


"Not hibernating automatically" (showing "Lux Lite"): This shows you've got the last word which apps Greenify shall deal with. In fact, without you doing so, Greenify won't deal with any app.
"Will hibernate in minutes after screen is off" (showing Evernote &amp; Co): This is one of the ways Greenify can deal with apps: things which do not need to be active while you switched off your screen can be sent to sleep (though the selection in the screenshot seems weird to me: I'd never put my automation app – here IFTTT, in my case Tasker – into this section)
"Hibernated" (showing "Amazon Kindle"): So the apps there are put to sleep, though the screen is on (otherwise this section wouldn't make any sense as you'd never be able to see it). These are the apps "put to sleep" whenever they're not running in foreground: why should an eBook reader (here: Kindle) be active when you can't see it (unless it's using TTS to read a book aloud, of course)?


Greenify comes for free and doesn't require root to work (see top of second screenshot: "Working Mode: Non-Root") – though it unleashes its full powers with root, its Donation package, and the xposed-framework.

If you want to learn more on this app: there are currently over 70 answers mentioning it, feel free to browse :)



1: before I complemented my answer with this information; see e.g. comments on this other answer