That's a fair few extensions.
Nice theme though, quite minimal.
I like minimal, as you can see.
I'm using Menu Editor mainly because I tried to do everything I do with this extension now (hide everything I don't use) with the userchrome.css file. However, I made a right mess of it and couldn;t find out how to hide most of them.
I did hope that this extension would edit this file, and then I wouldn't have to use it again.
But, no such luck.
I'll give the css file another go when I get my laptop back though, before resorting to this extension again.
I don't find it slows Firefox's startup at all, on this laptop (1.4GHz Celeron M, 512Mb RAM, 40 Gb 5400rpm HDD) Firefox starts in around 5 seconds.