Yahoo mail is very buggy. It keeps jumping to huge letters/screen then back to normal. Does this everyday, many times a day.
Every day yahoo mail screen behaves erratic. Goes from normal screen to really big letters/screen and then back to normal again. It's unresponsive while this jumping of screen goes on. Jumps to huge letters and back to normal and does this multiple times a day. Hate it.
If needed, take a look at the browser troubleshooting steps in this article to see if that fixes the issue.