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. 