Smaller browsers built on webkit do exist; see ‘Epiphany’, ‘surf’, ‘luakit’, and ‘Nyxt’.
Qt’s web component used to be based on webkit as well, though they’ve switched to Blink (Chromium).
Unfortunately, none of the browsers listed above are 100% sufficient to replace Firefox. They all rely on GTK bindings on webkit, which has its own quirks; and none have support for webextensions.
Smaller browsers built on webkit do exist; see ‘Epiphany’, ‘surf’, ‘luakit’, and ‘Nyxt’. Qt’s web component used to be based on webkit as well, though they’ve switched to Blink (Chromium).
Unfortunately, none of the browsers listed above are 100% sufficient to replace Firefox. They all rely on GTK bindings on webkit, which has its own quirks; and none have support for webextensions.