I have to apply for a lot of rentals (housing). The necessary websites are pretty invasive things (2Apply, snug.com, etc) and need access to local files for uploads of documents (ID, bank balances, etc). There's also a lot of copy-and-pasting between Thunderbird and browser.
I use Firefox with NoScript, uBlockOrigin and Containers (one container for each platform) in a virtual machine (Fedora).
I have a dedicated email alias with my provider for all this, and a dedicated calendar - I intend all to be handled in an instance of Thunderbird on the VM. But I still have to log into the server via Thunderbird with my 'initial identity' (i.e. my real email). So this data will sit in TB files on this VM - can they be read?
Also, I don't know how TB will handle this. Will it download all email headers and then discard all but the folder I want - in which case, could they still be eavesdropped on by one of the platforms?
I don't even understand enough to know if I am right to worry. If a website has scripts that allow browsing your computer to find a file and upload it (or drag and drop), can it go snooping around in other folders, like TB's?
Both are Mozilla products, do they interoperate? will Firefox obtain my real email address login from TB and exchange it with the websites?
Have read things about sandboxing on both Firefox and Thunderbird, and its not left me reassured.
I understand there is firejail, which I've used before but I found it poorly documented, and files transfers could be a nightmare. I really need fluid transfers and even copy-and-paste has to work well.
After all, I am using a VM, which is isolated already. I'd like to leverage that first.