When including certain percent-encoded characters in the open_url value, the browser does not open, and no errors show up. The loading circle appears very briefly next to the mouse, as if something should have happened.

When running a command like

/execute as @p run tellraw @s [{"text":"%2F '/'","color":"yellow","clickEvent": {"action":"open_url","value": "https://abc%2F"}}]

and clicking the text, the browser does not open. This of course happens without 'abc' as well.

When the command includes a percent-encoded 'A' for example, the browser still opens, albeit with it displaying an error as the URL does not exist.

/execute as @p run tellraw @s [{"text":"%41 'A'","color":"yellow","clickEvent": {"action":"open_url","value": "https://%41"}}]

Including any of the following characters anywhere after the '//' results in the browser not opening.

%2F '/'

%3F '?'

%5C '\'

%00 null

I believe with (probably) every other character, at least a new browser window opens, even if the URL isn't navigated to.

Using Firefox, in case this is somehow different between browsers.