A window "…pops up and says I have malware, to run a scan…" is quite different than a window that pops up saying your browser is out of date. I get the "your browser is out of date" message sometimes at FB and a couple of my financial institutions. Usually, one can just continue. On the other hand, a window asking you to "click here to run a scan" (including a window for Mackeeper) almost always will result in one downloading malware or a very intrusive app that is usually almost impossible to get rid of. The old saying, "never download stuff from unknown sources" applies. FB is intrusive itself (keeping track of stuff you do on the interweb); but I don't think even FB itself has "scanware".
QuickTime: Rotsa ruck going to 10.7, 10.8, 10.9 unless one's puter came with it. Far as I know 10.6 users can only download 10.10. However, far as I know, it is true that updating to a later OS is the only way to update Safari. I updated to Yosemite on an external HD and I'm not very enamored with it.
Much: I'm like you, I prefer Safari. But...