The future problem with Firefox's Electrolysis project
Firefox Electrolysis ('e10s' for short) is a project to push Firefox towards a multiprocess model like Chrome's. This is both a daunting amount of work and a praiseworthy goal with a number of benefits, but there is a problem lurking in the future and that is Firefox addons.
The direct problem is that any number of addons are not Electrolysis compatible for technical reasons. Firefox developers have partly worked around this with shims, but shims are an incomplete solution and can't make all addons work. Checking arewee10syet makes for depressing reading much of the time; a great many popular extensions are not working under Electrolysis (including NoScript, one of my critical extensions). It seems quite likely that a number of reasonably popular extensions will never be updated to be Electrolysis compatible and so people will be faced with a choice between not getting Electrolysis or abandoning them (the likely choice here being 'don't go e10s').
(The popularity of an addon has no relationship with the attention and spare time of its developer(s). There are any number of popular addons that have basically been abandoned by their developers.)
The indirect problem is that at some point Mozilla is going to want to turn Electrolysis on by default in a released Firefox version. In a straightforward version of the switch, some amount of reasonably popular extensions will partially or completely stop working. If people are lucky this will be obvious, so at least you know that you have a different browser now; if people are unlucky, the extension will quietly stop doing whatever it does, which is bad if this is, say, 'protecting me from some sort of bad stuff'. There are various things Firefox could do here to avoid silent breakage, like not enabling Electrolysis unless all your addons are known to be e10s compatible or warning you about some addons perhaps breaking, but none of the options are particularly good ones.
(Well, they're not particularly good ones if Mozilla's goal is widespread Electrolysis adoption. Mozilla could take the safe conservative approach if they wanted to; I just don't think they will, based on past behavior.)
When this future comes to pass, knowledgeable people can go in and turn off Electrolysis in order to get a fully working browser back (at least one hopes). Other people, well, I suspect we're going to see a lot of quietly or loudly upset people and Firefox is going to leak some more browser share as well as seeing some more people turn off Firefox automatic updates (with the resulting damage to security).