Most extensions take data from your computer and send it to their server in the Cloud to do the work. From a developer’s standpoint, that’s the easiest and cheapest way to create and run an extension.
Extensions that look at the text or document you’re looking at — a text-to-speech reader, adblocker, a summarizer etc. — indiscriminately vacuum-up all the information that a user is reading and let the tools on their servers do the processing e.g. turn text into speech or apply algorithms that pull out the important ideas, shutdown ads etc. They then send that processed information back down to the local computer.
Think about what that means. All of what you are browsing, all the pages of all the sites you visit, are sent to a server somewhere and stored.
Easiest way — not necessarily the best way or the only way
This is not an inherent limitation of extensions.
Extensions can be built to work on the local computer and do a lot of functionality even if they are disconnected from the internet. In the same way some iPad apps are really just portals to external servers and and other apps are a program running on the local iPad.
So the first key question you should ask your extension developer/provider:
“Is your functionality done on the computer or in the cloud?”
My guess is that most of the time the answer will be “the cloud.”
Don’t take that as a sign of sinister intentions. It’s just that from a programming and software development standpoint creating an extension that does key work on the computer and not totally in the cloud is actually much harder and time consuming.
“That’s okay,” you might very well be thinking, “I only use an extension when I’m looking at curricular texts. Not personal stuff. Who cares if some server has stored my research on “Cootes Paradise and Wetland biomes” or the “Riel Revolt?” What I’ll do from now on is keep my extensions off if I’m looking at anything personal, or private student information (IEP, marks etc.) Better yet, I vow to only turn the extension on when I actually need to use it. I’ll keep it off by default.”
That brings us to… When is your extension not working?