Right now, if I try to visit any page on English Wikipedia, I get a JS exception thrown:
[Exception... "Persistent storage maximum size reached" code: "1014" nsresult: "0x805303f6 (NS_ERROR_DOM_QUOTA_REACHED)" location: "<unknown>"]
This is despite the fact that I currently have nothing in localStorage for English Wikipedia and my localStorage quota is set to the default (5 MB).
I think what's going on is that Firefox is sharing localStorage space across all wikipedia.org sites, and since I have several ~1 MB MediaWikiModuleStores from other Wikipedias, it doesn't have room to store one for en.wiki. See https://support.mozilla.org/en-US/questions/963825 for someone else who noticed the same problem in Firefox but for a different website.
One possible semi-solution to this bug is discussed in bug 64721. Even if the size of MediaWikiModuleStore was reduced, however, you could still run into this problem if you visit enough Wikipedias.
Version: 1.24rc
Severity: major