Does Firefox, Chrome, others have a low integrity cache area like IE's Content.IE5?
%localappdata%\Microsoft\Windows\Temporary Internet Files\Content.IE5
%localappdata%\Microsoft\Windows\Temporary Internet Files\low\Content.IE5
..I've moved that appdata folder so much but I'm actually not sure of its contents..
What do you mean by "moved"? Where?
No moving here - I delete the content.ie5 sub-folders.
Whether it is me or my systems, no idea -- but when the IE cache gets filled -- ~0.5 GB or more, strange things start to occur like corrupted zip downloads (<5 mb from a forum other than Sysnative), I delete them usually via batch or VBS scripts.
IE will create the sub-folders under each content.ie5 folder as needed.
I have found IE cache files in %localappdata%\Microsoft\Windows\Temporary Internet Files\
Virtualized
Also, IE cache & cookies in %tmp% - no idea why.
... I'll I know is if I want to keep my addon's and history for FF that's the place it is.
Under
%localappdata%\Mozilla\Firefox\Profiles] --?
All I have are profiles that look like -
vb0w7bmb.default -

Are the bookmarks, add-ons & history in there somewhere?
I never had to back up anything in Firefox before.