There are a few sites where I can select text and get a popup, but when I click on the icon, there is no response at all. For example

asahi.com

sankei.com

etc.
Is this difficult to fix?

Works even on phone in distinction to Swift Selection Search

Swift Selection stopped working a while back and I was forced to find an alternative. I'm SO glad the developer forked it! This one works much faster/better options!

Please keep update this great extension.

The best search extension!

Excellent, thanks to the developer

This is the power user search add-on you've been looking for. The add-on is already extremely powerful and feature rich and has many time saving features, and it's still growing. I absolutely love it! The developer is very friendly and likes to work on suggestions from users. I can only recommend. The current developer forked SPC after its precursor add-on, SSS (swift selection search) was abandoned (the developer stopped working on it). A lot of powerful features have been added, such as POST search. Adding a new search engine is quick - just right-click on the search engine's input box and select "SPC - Add search engine". There are performance improvements: for users with very many tabs, SSS used to freeze for several seconds when you edited anything in the options. The developer of SPC fixed that in short order after I reported it.

If you use this add-on, please make sure to donate a little via the "Contribute now" button on the Mozilla add-on page!

Excelent add-on. I would give it the 5 stars, but it bugs me that the license says it is GPL, while the git repo only contains instructions and readmes, and the XPI file contains unreadable minified files.

I've been a long-time power user and fan of the original SSS add-on this add-on is based on and recently discovered this fork (SPC). It's awesome! SPC perfectly addresses the few remaining niggles I had about SSS. I now use this instead!

I'm not a fan of how the context menu option will always default to the clipboard when nothing is highlighted, but after importing my search engines and getting used to the pop-up, I think this might be one of the best add-ons of it's kind I've experienced yet.

Хорошее дополнение. Подхватывает search.json.mozlz4 и есть функция добавления поисковой системы через ПКМ. Всё очень чётко и удобно. Спасибо.
// Спустя 5 лет как был лучшим так и остается. Все остальные альтернативы через чур мудрёны в плане настроек и всяких кодов и совместимости. Тут всё как делалось так и делается в пару кликов.