Why so much "chrome" on my computer?

Firefox has been using chrome manifest files for years...
HubLog: How a Firefox Extension Works
...so, just having FF installed is going to get you several files with chrome in the name.

And you will be seeing a lot more of that:
Mozilla sets plan to dump Firefox add-ons, move to Chrome-like extensions | Ars Technica


Some of the other folders were from AVAST. Probably not a problem.

Consider that the word "chrome" also has multiple different meanings that are used more or less frequently on computing (in addition to other fields too), which can easily justify the appearance of the word in other, totally unrelated files.
In particular, the references to "chrome" for meaning parts of GUIs used widely outside the web browsers so it won't be difficult to find it in other files.