It can be ๐
I also didn't have a need for it and wanted to disable it and I found browser.tabs.hoverPreview.enabled
in about:config
(set it to false to disable).
There's also browser.tabs.hoverPreview.showThumbnails
to only disable the image preview but not the new layout of the tooltip (there's also a corresponding option for it in the main settings)
Just adding that as I understand this, donations to the Mozilla Foundation cannot go towards Firefox, because it's [edit: Firefox is] actually part of the Mozilla Corporation. To help with funding Firefox people can consider purchasing the Corporation's other products (VPN/Relay/Monitor), or purchasing merch.
See more here on the AMA on Reddit, and this thread