Let's attack the performance issue first. Since the following issue is "of the moment," let's start here:

e10s

One of the headline changes in Firefox 48-49 is e10s, which separates the browser interface process from the page content process. Yes, this moves content into plugin-container.exe causing it to use much more memory. The performance impact of this can vary a lot between systems: many users find it faster, some find it slower, for many it's neutral. Hopefully by the time all the kinks are worked out it will work smoothly for everyone.

Are you using e10s?

You can check whether you have this feature turned on as follows. Either:

• "3-bar" menu button > "?" button > Troubleshooting Information
• (menu bar) Help > Troubleshooting Information
• type or paste about:support in the address bar and press Enter

In the first table on the page, check the row for "Multiprocess Windows" and see whether the number on the left side of the fraction is greater than zero. If so, you are using e10s.

If you are using e10s:

To help evaluate whether that feature is causing this problem, you could turn it off as follows:

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button promising to be careful.

(2) In the search box above the list, type or paste autos and pause while the list is filtered

(3) Double-click the browser.tabs.remote.autostart.2 preference to switch the value from true to false

Note: the exact name of the preference may vary, but it will start with browser.tabs.remote.autostart

At your next Firefox startup, it should run in the traditional way. Any difference?

Hopefully that will settle things down but, if not, see also: Firefox uses too much memory or CPU resources - How to fix.

Bookmarks

What have you tried to recover your bookmarks so far?

The Refresh feature usually creates a folder on your desktop named Old Firefox Data and puts your entire old profile folder inside (the folder containing your Firefox data such as bookmarks, passwords, etc.).

If you click into there, can you find a folder named bookmarkbackups containing files with names like this (9876 represents the number of bookmarks backed up in this file):

bookmarks-2016-11-04_9876_gibberish==.jsonlz4

Firefox's Restore feature can apply that backup to your currently running Firefox. This article has the steps: Restore bookmarks from backup or move them to another computer (to open a backup from the desktop, you'll need to use Choose File and guide Firefox all the way to it).