That is on facebook, under my icon where I log out.
That just looks like slow or aborted loading of the element. Possibly due to network issues at their end? (Or a slow connection more generally?). Does it happen every time?
Note I don’t frequent those sites, but it does happen to me too, on occasion, with others. 
It rarely happen, rarer what I type when leaving a message on a post before a share is just *s when I type. The sitrre is fine, just when I type. Facebook has issues, no other site does that.
Could be the facebook server, could be your internet, who knows. Some script is not loading. In theory could also be your adblocker.
I know in Firefox in strict privacy settings Facebook will do this, among many other sites. A refresh every session would temporarily fix it for me.
Brave/Vivaldi (and probably most other Chromium based browsers) did not do this.
Whitelisting Facebook, or not using strict privacy would also most likely fix it. 
Could be the facebook server, could be your internet, who knows. Some script is not loading. In theory could also be your adblocker.
Only started a few days back. Off topic, bummed about Reddit, great idea but, poorly executed.. It is like the owner told his 8 year old to build it.
Maybe try clearing your browser cache, or if this doesn’t help, trying with a fresh browser profile? (Are you actually using Firefox, or something else? It always helps to state which one(s)).
Browser Safe Mode (somewhere in the help menu) will rule out extensions as a reason of the blockage.
I am having the impression that Reddit is populated by 8-year-olds. 
I am unable to duplicate this issue.
I don’t use Facebook… and recommend you stop too.
I notice these symptoms often with Facebook and YouTube.
I believe they often like to switch things up so that generally a rolling bug affects at least 20% of users at any one time, but when they report it then 80% of users can assure them that it’s just them being paranoid.
Me too Click 
I agree, it looks like 
My monitor or Manjaro?
My guess would be neither.
The easiest way to test is to open a new tab and load another site. If another site is also apparently struggling to load, perhaps the problem is with the browser you are using.
To test that theory, try another browser with the same sites – a process of elimination.
Once you have solid and actionable information to share that positively points to a culprit – only then – create a Support topic.
It is your monitor - or your network - not Manjaro.
This would be my guess as well..
I have a good stable fast connection, it is facebook. Other sites are fine so far.