Add temporary Firefox add-on alert
Created by: tjkandala
Closes #14233
This component won't render anything after December 21, 2020.
@AlicjaSuska I interpreted "display this alert for all users" as "show this alert for users that have already dismissed the usual alert as well". Since this alert isn't meant to replace the original alert (under this interpretation), I made sure that the two alerts didn't look too bad together.
Only the Firefox alert
Both alerts
I decided that it wasn't yet time to create an abstract <RepoAlerts>
component, since this is only the second alert and it's temporary.
'install the add-on' links to our docs page instead of the direct download link, since that would feel sketchy and provides no further context.
I also added
- snapshot tests to assert that this component only renders before the final date and that it doesn't break when passed unknown external URLs
- stories for all code hosts so you can easily check the copy.
All this code should be ripped out after December 21, 2020.