Don uses Chrome, and his browser page will freeze when he uses Gmail. But if he closes it, he can use the browser. Leo says that tabs are sandboxed in Chrome, so Google may see that the tab is running in the background, and as such, it's freed up resources through "tab freezing." It's a recent feature of Chrome. You can turn it off, but it does free up memory and resources for your computer. Make a new tab and type "chrome://discards." This will give you a list of suspended tabs. Type Chrome://flags to turn it off. Here's how - https://www.techradar.com/news/chromes-new-feature-will-stop-tabs-from-eating-all-your-ram-heres-how-to-try-it. This gets you to the secret preferences menu.
Another option is to remove Chrome and reinstall it.