I marked the answer above as unhelpful, because the issue raised in the title of the question went unanswered by it: English not showing up in the preferences, i.e. the language selection dropdown menu didn’t have English. I was able to fix this by unselecting Google and Google Services from HTTPS Everywhere’s settings, but then again wasn’t able to reproduce it after re-enabling them, so I’m still not sure whether HTTPS Everywhere was the root cause.

For me, the same symptoms were caused by apparent incompatibility btw Greasemonkey and another add-on, autoHideStatusbar, so you could try disabling other add-ons.

I just tried this in Shiretoko (4.0b2pre) and it’s fixed there, i.e. the plus sign is preserved. So you probably deduced the right culprit. :)

As the summary says: when a user opens a new, empty tab, it opens next to the rightmost of tabs currently open in the browser. This is inconsistent with the way links in new tabs are opened, which is to have them next to the currently active tab.

Steps to reproduce:
1. Open multiple tabs in the browser.
2. Select the leftmost tab.
3. Press Ctrl + T.

Expected result:
Have a new, empty tab next to the leftmost tab.

Actual result:
The new, empty tab opens next to the rightmost tab.