IMO this "feature" should be disabled!

via:

about:config browser.chrome.

browser.chrome.favicons;false browser.chrome.site_icons;false browser.chrome.image_icons.max_size;0

I never liked this feature anyway. In addition to finding questionable privacy/security issues in the past, if it's enabled and you bookmark websites it inserts a bunch of garbage into the bookmarks for that bookmarked site and just increases the size of the bookmarks file if you keep it.

I'd just configure it per above in future versions of TBB.