Next/previous tab commands don't work if the tab you're in is loading or one of the Firefox config/profiles/preferences pages, nor, weirdly, can you move from the rightmost pinned tab to the leftmost unpinned tab. This left/right tabbing was why I installed the plugin, having used Firefox's built-in option to redefine ctrl+tab to point to the last-visited tab. Not a deal-breaker, but I'm going to seek out something better.