An interesting problem surfaced on the old Opera presto.
If you enable the "Automatically add missing Icons" mode, the icons disappear, and after the mode is disabled, they do not appear.
While the solution is to disable "Only use CSS for selected weight", then everything works almost normally (the search icon disappears immediately after activating the plugin, but the rest work normally ... probably).
If the plugin is reinstalled with the default settings, then the "normal" icons are displayed.
Probably found a bug, please check.
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Update. Icons do not return to their normal state when "Automatically add missing Icons" is disabled, if the logging mode is set to "INFO". If Error mode is enabled, the icons will be restored.