Recently I've had character I type stop appearing and I realized it happens when a right-side ad reloads. It doesn't happen with catawiki ads while creating this post, but it happened twice this morning (so far) when typing a private message with an ad for Toyotathon/KBB in an ad series that changes every 30 seconds. (But not every ad in the series caused the problem.)
What information should I try to get if I see this again?
Using Firefox on Ubuntu.