Mozilla Firefox keeps sending download instructions - interesting - instructions to download what? It might merely be asking you to download the current version. Firefox releases a new version every six weeks (I think), but often releases security/performance fixes in between. Like everything else, it needs to be kept up to date in order to remain reasonably secure.

Check your Firefox update settings for more information - on the Windows version, I think it's under Tools > Options and so on.

If the download instructions are not Firefox related, it might be time to do a couple of scans with your antivirus, with Malwarebytes and with AdwCleaner.

As for Chrome - hmmmm. If you like that sort of thing... It's a good enough browser, but it's very much Google, with all that that implies with respect to your privacy. At least do your homework first with respect to its settings, and resist its demands that you log into Google and stay logged in. Unless you genuinely find the tracking and profiling useful - I assume there are some folk who like that sort of thing.