Same experience as user 15218768. This add-on (v6.2.0) creates massive loss of performance (major lags) on all Google-related pages in FireFox.

This extension works well on research sites, but it causes serious performance issues on pages like Amazon and Google when used with Firefox on macOS in Low Power Mode. I ran Firefox Profiler and confirmed that the extension injects scripts that run heavy regular expressions in the background, blocking the main thread and causing tabs to freeze or load very slowly.

Disabling the extension or exiting Low Power Mode fixes the issue. Until this is addressed, I recommend only enabling the extension for specific research sites.

The firefox version of this extension lacks certain crucial features that make it rather useless. For example, one basic function that it lacks is the ability to save pdf files directly to my library from firefox's in-built pdf viewer. Instead, the extension merely saves the url to my library. I would encourage the developers to add the same functionalities to the firefox extension as those on the chrome extension.