All seven features are built into version 1.4.0 for both Chrome and Firefox, at the same version number. I tested each one in Chrome and Firefox. Most tests used a stand-in translator, because the online services were blocked in my test setup; a final check of the actual Chrome zip translated real Korean pages to Spanish correctly. Firefox on Android wasn’t retested this time.

Auto-detect the comic’s language: when “From” is set to Auto, it looks at the first few pictures and works out the language itself, even if the website is in a different language. The popup then shows something like “Auto-detect (Korean)”. The answer is remembered for that series for a week.
The first time on a new series, the first pictures wait about 10 seconds while it figures this out.
It assumes one language per series, so a mixed-language page will use the main one.
Click a bubble: clicking a translated bubble opens a small window with the original text, copy buttons, a box to fix the translation (the fix is kept) and an “add to glossary” box. You can turn this off in Behavior.
Names glossary: in Translation settings, one rule per line, like 강남 = Gangnam. It applies before and after translating. When you change it, pages already open update straight away without reading the pictures again.
Translate an area: press Alt+Shift+S, use the button on the floating panel, or right-click → “Translate an area of the screen”, then drag over any part of the page. This is desktop only.
Picture under the mouse: Alt+Shift+Y translates just that picture.
Sound effects: a switch to translate them or leave them as drawn. It guesses what counts as a sound effect (one short word drawn on the artwork), so it won’t catch every case.
DeepL: add your own key in Translation settings and DeepL is tried first, with the usual engines as backup. A free DeepL account works.

All the new menu text is translated into the 21 other interface languages, and the “What’s new” note lists these features.

The store docs include the new Chrome and Firefox descriptions, release notes for 1.4.0, and an updated privacy policy. The policy now covers DeepL, the screen capture for area translate, and the glossary being kept on the device. The extra-languages zip hasn’t changed, so keep using the one you have.

NEW in version 1.3: the next chapter is translated in advance while you read, so it opens already translated. Plus: read aloud, faster translation and vertical Japanese and Chinese text.