Very useful.

Some suggestions:

The address bar indicator is superfluous, we already have the tool bar button. Please add option to remove the address bar indicator. Or omit completely.

It seems impossible to set the zoom for a page
*but not its subpages*. Please add a way to set "this level" only.

Similarly, add an option please to discrimination between pages of the same level. Use case: A forum with the topic index "...path/to/forum/index.html" and the topic threads "...path/to/forum/topicNNN.html". The index is often a list of natively large headlines, while the topics have natively a smaller text. Is would be great if the index could be made smaller (for quick scanning -- more rows on the screen), while the topic threads could be enlarged for better reading. There must be many other use cases for such a feature, I'm sure.

From an information ergonomics perspective, reduce the cognitive load of the need to translate from symbols in the subsite popup menu to their meaning. A plain text menu that nobody has to learn the meanings of would be more elegant.

If I understand it correctly, the level settings are set from a loaded page. Then the text "include all descendants except for the first X levels" can be shortened to "Apply to this page and its descendants", or even "This page and descendants".

Also great would be an option for deeper levels to overwrite the settings for levels higher up. So we get an overwrite hierarchy for level-specific settings (">" means "overwrites"): deepest level > deeper level > deep level > subdomain > domain > default. (Do not set levels by fixed numbers here, only compare depths, because there are incredibly deep paths out there that would make a menu ridiculously long.)

And, a BIG THANKS for your work already done here!