Used to work great, but after closing and reopening it doesn’t work

I’ve had this on my computer for a while, and it’s always worked great. I love it because I often need to have multiple gmails open at once, and this was good to keep my personal email seperate.
Today, though, I was having an issue writing an email, so I quit the app and reopened it for the first time. And everything fell apart. The text is way to small. I’m getting an error message saying that it’s based on an outdated Safari. It doesn’t have the indication of how many emails are in my inbox on the bar now. I can’t attach attachments to emails. It’s just a mess.
It’s a shame, because it was workign perfectly before. Now I have to find something new.
It gets three stars because it used to work.

Saria0215 about App for Gmail