If you're on a modern Android device, you might have encountered the problem that Facebook refuses to show your private messages and instead insists you should install their Messenger app, which is bullshit.
When your browser connects to a site it sends a useragent string, which is used mostly for statistics, but sometimes also to identify the capabilities of your device and serve customized content. Some sites (e.g. Facebook) gets this all wrong by providing a less useful version of their site.
There's a simple fix, at least if you're using Firefox. By spoofing your useragent, you can trick sites into believing you are using another browser than you really are. We want the site to serve us the mobile version, but still pretend the client is too old to be able to install apps.
These instructions were written for Firefox 57, but should probably work on older/newer versions as well.
about:config (just type it into an empty tab).+ and add the preference general.useragent.override. Click the Boolean field and change it to String.Mozilla 5.0 (Android; Mobile; rv:40.0) seems to work (as of january 2018). There's no copy-and-paste in the config dialog, but it's short enough to type by hand.
There is also an alternative solution:
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