The problem is that when this property is checked/on, hovering on a tab sometimes does not show the preview.  In this case it seems that, in order to regain this capability, it is necessary to click-out of Firefox, or even to re-start or shutdown my computer.  Any of these solutions make this important capability essentially unusable.

       I have observed this problem with Firefox on my MacBook Pro (2.8 GHz Quad-Core Intel Core i7) running MacOS 10.15.7 Catalina.

       This is such an important capability because in an arbitrarily complex tab environment it provides a naturally fast and efficient means of providing enlightening snap-shots of the current state of Firefox.

       Are there any other settings BESIDES 'General > Show an image preview when you hover on a tab' that need to be checked/on (or maybe even unchecked/off) in order to ALWAYS show the preview when hovering on a tab?

       Thank-you very much for looking into this issue and, if necessary, updating Firefox so that this capability ALWAYS functions as expected when it is checked/on, at the earliest possible convenience.

The feature 'General > Show an image preview when you hover on a tab' is just a really great piece of work from Mozilla. I believe this fabulous feature first became available in the current version of Firefox, which is 131.0 (64-bit). The problem is that when this property is checked/on, hovering on a tab sometimes does not show the preview. In this case it seems that, in order to regain this capability, it is necessary to click-out of Firefox, or even to re-start or shutdown my computer. Any of these solutions make this important capability essentially unusable. I have observed this problem with Firefox on my MacBook Pro (2.8 GHz Quad-Core Intel Core i7) running MacOS 10.15.7 Catalina. This is such an important capability because in an arbitrarily complex tab environment it provides a naturally fast and efficient means of providing enlightening snap-shots of the current state of Firefox. Are there any other settings BESIDES 'General > Show an image preview when you hover on a tab' that need to be checked/on (or maybe even unchecked/off) in order to ALWAYS show the preview when hovering on a tab? Thank-you very much for looking into this issue and, if necessary, updating Firefox so that this capability ALWAYS functions as expected when it is checked/on, at the earliest possible convenience.