I like the new Firefox, but for some reason it seems to have a terminal inability to remember new book marks. Which is a pain to say the least, fortunately, I'm just using bookmarks to bookmark my progress on a web comic I'm catching up on. Still an inexcusable bug to have.

EDIT: Never mind, apparently now the bar limits the number of results it shows, not guaranteeing that you see the bookmarks if you've too many matches. Still a boneheaded bug.

Then I think we are talking about different behaviours. The only time Firefox doesn't load tabs immediately for me is when it is restoring sessions on startup (because I have that option on).

Exactly, the Don't load tabs until selected option only refers to the start-up behaviour of the browser, not when opening a new tab.

For example if you have When Firefox starts set to show my windows and tabs from last time and the DLT is checked then only the current tab is loaded, which means that the browser starts faster than if it had to load all the tabs you had open when you quit the browser last time.

As for SPDY, it should have absolutely nothing to do with your download issues, because the website/server you're connecting to has to understand and use SPDY, otherwise it just uses HTTP.

Also, SPDY isn't used for actual data downloading on any servers that I know of.

You can always disable SPDY temporarily, and test if your problem persists (but I doubt it's the cause):

Open about:config and set network.http.spdy.enabled to false. (Don't forget to turn it on back later). You can also install SPDY indicator to see if some site actually uses it or not.

I had issues with downloading big files from GOG before, so I just use wget or curl for that, with the correct referer (which you get when starting the download in the browser). That works OK, since you can make them resume the download if it breaks.

For example:

curl -C- -o <filename-to-save-as> --referer <GOG-provided-referer> <download-url>

If this breaks, just rerun it, and it will resume from the point where it broke off.