To say that I was unprepared for this development would be an extreme understatement. While I do continue to believe that one day, I'll get to finally doing the LJlogin 3 rewrite, I'm nowhere near ready for it, with a couple background projects I need to get done before I start looking at it.
That said, all hope is not lost. There are options for plugging the leak and keeping the ship that is the current gen of LJlogin afloat in the brave new world of Firefox 29. If all you want is just to restore the add-on bar so you can keep on LJlogin'ing, there is the The Addon Bar (restored) extension. If you want a big hammer to quash all the fancy new style updates, have a look at the Classic Theme Restorer extension. I've tested them both, and either one works just fine.
(I did not test them together. Probably best not to chance it.)