It appears that LastPass works fairly well with e10s. It seems to fill in forms ok. It doesn't get you into the vault on startup if you have that optioned enabled.
Perhaps the biggest problem is that it hangs and crashes Flash very often. I did extensive testing with a clean Firefox profile and narrowed this problem down to LP. I tried the latest pre-build but that didn't help. Btw... the new pre-build turns all my context menus white and there is no select highlight color anymore. This happens in both e10s and non-e10s.
So it seems LP is almost e10 ready out of the box. The Flash crashes though are preventing me from using the e10s.
Another thing to point out is that there are two ways to run e10s. One way is to use the option in the File Menu to run e10s in a new window from a non-e10 window. The other is by enabling e10 permanently via the Options Menu. Be aware that these two methods are not equal. As an example, if I run an e10 window LP will not fill in any forms/passwords etc. My LP sites don't even appear on the LP context menu. However, if I enable e10 as my default, form fill does work and my sites show up in the LP context menu. The point here is that people reporting problems, as I did, might be running in an e10 window and therefore will have all the problems I mentioned. The only way to run e10s properly is by permanently enabling it.
With all this said it seems you might have an easier job to make LP e10 compatible. You seem almost there.