It is simply a way of letting the user know the webpage is encountering errors or slowing down their computer. You can submit feedback to the ff dev team here:

https://qsurvey.mozilla.com/s3/FirefoxInput/

Hello Bill Mayhew,

To disable this bar, would you try this please :

Type in the address bar about:config and press Enter. (ignore the warning)

Type in the search bar processHang and look for these two preferences :

dom.ipc.processHangMonitor and dom.ipc.reportProcessHangs

Change their values to false

Then close and restart Firefox.

I hope that will do the trick ....

Also : following Eve's advice will be an excellent idea  !

You can check the Firefox Task Manager (about:performance) and about:memory pages.

• https://support.mozilla.org/en-US/kb/task-manager-tabs-or-extensions-are-slowing-firefox
• https://support.mozilla.org/en-US/kb/firefox-uses-too-much-memory-or-cpu-resources

I don't object to a *reasonable notification* but the yellow bar was/is SERIOUS overkill!! Hoping 75 has improved this.