Add feature to the toolbar that would show general on-page elements like Title, desc, subheaders, canonical, hreflangs, OG, etc.

One of the most important ranking factors aside from link building is content word count. I use a toolbar called Serpworx (you might want to check them out) and one of the most important metric I've been going to recently is their word count metric. If the top 3 spots on the SERPS have over 1,500 words then we know we have to build a 2,000 word page. Next to DA or UR this is my goto metric.

I wonder why the option wasn't built-in, because it is a known thing for chrome extensions, people often do not want intrusive behaviour by the extensions so the majority of extensions using numbers on the icons have to ability to hide them. Millions of years of evolution, we were hunters, so everything that moves like that is distracting. That is basic UX, notifications and moving things are the most powerful and the most annoying thing, that is why people have the ability to customize them. A moving thing like numbers with that bright orange there clearly makes you watch with your peripheral vision and breaks your focus and flow. All extensions like AdBlock Plus, AdGuard and many more that like numbers on them, have the ability to disable them as they know that.›

Check for on-page SEO issues (like a very short description or a missing canonical tag) and suggest improvements

Is it possible to add another option to the toolbar to include metrics for the sub-folder you are in (when applicable)

Ahrefs Toolbar could show keyword suggestions for the search query in the SERP directly.

Age and Google Index (count of website pages) are important info for analysis. Please add these metrics.

Is it possible to also extract serp features with the search results csv export such as featured snippets, top stories, image packs. etc

Is it possible to add functionality that allows a user to search from a particular country/region/city. etc?

An advanced and user friendly SEO toolbar for Safari & Firefox is much essential in the backdrop of high ram consumption issue with Google Chrome & more over the number of Mac users have increased enormously.