I realized today that I could not edit tag filters from the sidebar on the home page. Clicking the 'edit' link beside the "Favorite Tags" header simply did nothing. Experimenting with disabling various browser addons did not help. I traced the problem to a line in the Firefox console "TypeError: localStorage is null (full.en.js:139)". Temporarily enabling "localStorage" in Firefox fixed the problem. However, I'm sure this is a bug, because whether localStorage is enabled or not, the tag filter works perfectly (indicating that the tags are not stored in localStorage), and as I later found I can edit the tags fine from the other UI for them on the user preferences page.