Unfortunately, mass download is something that has to be managed on client side (in your case by the Chunky app). The server alone cannot provide bulk download.
Sorry.

Hello,
To hide the navigation you have to either:

• press "Enter", if you have a keyboard
• tap/click in the center/bottom area (the empty one)

Let me know if you still can't exit the navigation interface, as this might be a bug.

Thanks for your donation. :)

Once a file has been scanned, it is not scanned again unless it has been modified or renammed. So the extra step of guessing the correct file type is done only once by incorrect file.
However, it happens once for each page when reading a comics using the online reader, so it's better to have correctly named files from the beginning (although the guessing step is very very fast).

I will not add a renaming feature to Ubooquity as it would go agains one of its core principles: "do not modify the files of the user", ever. But I have found a small tool that does just that: correcting the extension of CBR/CBZ files (it has a few other useful maintenance related features and is really simple, so it's worth a look).

The tool is ZenCBR.

Regarding performances, the current version has a bug heavily impacting reading performances when a scan is in progress. Perhaps that's why you experienced a problem.

I'll look closer at the code in charge of resizing the pages. You use Ubooquity 1.5.0, right ?

Regarding the button placement issue, I can't test it myself as the default Android browser does not exist anymore on devices running on recent Android versions (the official browser is now Chrome).
It could probably be fixed by generating better HTML/CSS than what I currently do, but if it only affects the default Android browser, I'd rather focus on other features.