You can select an area of the web page using the Capture search mode. The search mode can be set independently for the context menu and the browser toolbar from the extension's options.

You could also enable the "Use deep search when selecting images" option to continue searching with the Select URL or Select Image search modes. When enabled, the extension extracts all images from the clicked area, even if an overlay image was immediately found. If multiple images are found, you can select the one you need from a popup that lists the images along with their dimensions.

Hi, I'm happy you find the extension useful! You could also experiment with the options listed below to extract potentially larger versions of the image from the source code of the page. These options are not enabled by default because it takes a bit longer to download all variants of the selected image.

* Use deep search when selecting images
* Detect alternative image sizes

My impression is that you're using a fork of Firefox for Android that is customized to the point of breaking essential web APIs, but you'd have to share more details in a GitHub issue to figure out what went wrong on your device.

https://github.com/dessant/search-by-image/issues