Have you tried submitting patches for the aforementioned extensions? Having countless extensions that do the same thing is not in the user's interest, so we encourage collaboration wherever possible.

Extension 440 seems to be no longer maintained (according to the author), and they recommend moving to 876. However, 876 doesn't provide a url from what I can tell, so collaboration is not so easy. This version is a complete redesign, so a patch would just be to replace the whole project. Instead of trying to reimplement half of the Shell's features to produce the desired result, this one extends just two base functions that is used throughout the Shell. Also, inspecting their code shows that 876 suffers from a bit of bit rot since they haven't been updating the source to actually work with the newer versions of the Shell. I mean, they update the metadata.json, but extension.js still uses at least one function which has been removed since 3.10, so there are subtle bugs. If it's desired, I can hand over ownership/the url for this project to the author of 876, and let them update their 876 extension to use this version as their new base if they choose to do so instead. To be honest, this was more a experimental by-product of another (more larger) extension that I am working on, which provides "Workspace Groups" (you could say similar to "Tab Groups" in Firefox).

Hm, I messed with my installed extensions, and now this no longer works (I get a recursion error), even when I revert this to the one I submitted, so there might be something really broken with this that I didn't notice before.

Well, found the problem. I made a change to make sure this (hopefully) won't happen again. I made a few other improvements while I was at it too. Not sure how to update the version on here though. Also, I have sent a message to julo42, the author of 876.