(1) An easy way to download YouTube videos (preferably, any site's videos, but YouTube is the obvious target). There used to be several extensions that did this, but they all seem to have been broken by some recent change Google made.
(2) An URL rewriter: something that lets me set up a list of regex-based transformations to apply to any link I click on, redirecting me to the transformed URL instead of the original one. There are all sorts of uses for this, but the one that keeps annoying me on a regular basis is sites like DeviantArt that make you go through an "are you sure you want to leave our wonderful site?" page on every outgoing link. (I seem to recall something like this existing for Firefox, but it's been a couple of years since I used Firefox regularly and I can't find anything like this in a quick search of their addons page.)
I wish I had something analogous to Multifox, preferably operating on a per-tab basis.
I looked into making something of the sort, but unfortunately the necessary API calls (e.g. notify my extension BEFORE a cookie gets set) don't seem to exist, so any solution using the existing API would be a bit hackish.
EDIT:
It may be possible to do at the level of intercepting all HTTP requests in the affected tabs? (No idea if the API allows that, or if it would be a good approach even if it were possible.)
I see this being a hard one. I don't even know if that is possible, but I was asked by a designer a couple months ago and he even offered me some money to build that. Taking screenshots from a video source usually render very blurry images, so he was looking for an extension that would do good still images from a video at specified intervals or specific points in time. May be worth trying.
Not so much an extension, but I would love to be able to have Incognito tabs instead of Incognito windows.
When I'm doing web dev having two sessions in the same browser is great (ie. not needing another browser open), but I often only have one tab in the Incognito window. It would be very useful if I could just have an Incognito tab in my regular window.
Vertical/Tree Tabs like Firefox has Tree Style Tab.
Quick Tab is an...interesting take on the problem, but leaves so much to be desired. I'd pay money for a good Tree Tab system in Chrome. It is literally the only reason I still use Firefox for my daily browsing.
(1) An easy way to download YouTube videos (preferably, any site's videos, but YouTube is the obvious target). There used to be several extensions that did this, but they all seem to have been broken by some recent change Google made.
(2) An URL rewriter: something that lets me set up a list of regex-based transformations to apply to any link I click on, redirecting me to the transformed URL instead of the original one. There are all sorts of uses for this, but the one that keeps annoying me on a regular basis is sites like DeviantArt that make you go through an "are you sure you want to leave our wonderful site?" page on every outgoing link. (I seem to recall something like this existing for Firefox, but it's been a couple of years since I used Firefox regularly and I can't find anything like this in a quick search of their addons page.)