I recently upgraded IntelliJ IDEA from version 14.1.6 to version 14.1.7 due to their latest security update. Part of the update appear to be updates to their "built-in web server", which I've never used to my knowledge.
The upgrade seems to work fine, but now on occasion while I'm working I get a notification in the upper-right corner "Built-in web server is deactivated, to activate, please use Open in Browser". I haven't yet figured out what it is that I'm doing to trigger it, I think because as I'm working I'm not looking up there, and I only see it later.
While dismissing the message works fine and I'm happily continuing to work, I'm not sure what to turn off in order to prevent the message from showing up more. Is there some feature I've inadvertently told it to use and there is some problem with it?
There a question here on How to disable built-in web server but I'm not sure if that's talking about the same feature, and it's referring to a file URL whereas I'm testing my application in Tomcat using http, and as of this writing that question isn't answered either.
You can disable the notification in Preferences → Appearance & Behavior → Notifications → Built-in server. Set Popup to
No popup and deselect
Log if you don't want a notification in the log.
While I'm not sure why this happens, it seems that one cause is using the built in documentation tool (ctrl+Q (Win) / ctrl+J (Mac)).