I'm not sure what you mean by "double tab view." The only new thing I'm aware of relating to tabs is a new Show All Tabs icon that looks like a folder and shows between the New Tab + and the window minimise icons.

If it is that you are referring to you can get rid of it but not in a simple way. See: https://support.mozilla.org/en-US/questions/1466632#answer-1678349

Do you mean the thumbnail image that you see if you hover a tab?

There are two Boolean (true/false) prefs in about:config to control what to show when you hover a tab. This pref controls whether to enable this new hover feature or only show the legacy tooltip with the title.

• browser.tabs.hoverPreview.enabled

This pref controls whether to show a thumbnail or a two line tooltip with title and URL.

• browser.tabs.hoverPreview.showThumbnails

The latter can be controlled via "Settings -> General -> Tabs".

• https://support.mozilla.org/en-US/kb/about-config-editor-firefox