Tab previews are in the works for a future release of Mozilla Firefox. In current versions of Firefox you hover your mouse over a non-active tab (i.e. any
To control how fast/slow tooltips appear modify browser.tabs.cardPreview.delayMs. This is set to 1000 (milliseconds) by default, meaning tooltips only appear once you’ve hovered over a tab for at least a second.
From the article:
I saw that later, I guess I forgot to save the edit.
150 ms feels alright.