Ten seems low to me, but I haven't tested.

Meanwhile, could you confirm that the per-tab history depth of 50 has not been lowered?

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

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

(3) Scan down for the browser.sessionhistory.max_entries preference, which as you point out has a default value of 50.

(If you need to restore it to its original value, you can right-click > Reset it. Or you can double-click to enter a different value.)

Okay, I see now. There are some new preferences that you will need to adjust.

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

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

(3) Double-click the browser.sessionstore.max_serialize_back preference (default=10) and enter the desired number of pages you want to be able to go Back in a restored tab. I haven't checked the source to see whether there is a limit.

(4) Double-click the browser.sessionstore.max_serialize_forward preference (default=-1) and enter the desired number of pages you want to be able to go Forward in a restored tab. I haven't checked the source to see whether there is a limit.

Note to self: Bug 943339

See also:

• bug 943339 - [Session Restore] Cap the amount of history we save

• resource:///defaults/preferences/firefox.js

// number of back button session history entries to restore (-1 = all of them)
pref("browser.sessionstore.max_serialize_back", 10);
// number of forward button session history entries to restore (-1 = all of them)
pref("browser.sessionstore.max_serialize_forward", -1);