Firefox has been causing drops in my internet connection lately. PLEASE, PLEASE, PLEASE HELP!

Question

OK, I recently wrote to the author of Session Manager about this problem, since I thought I'd narrowed it down to that, but, well, maybe not. I'll copy & paste that conversation here, rather than waste a lot of time writing up something from scratch, especially since I've already wasted an INCREDIBLE amount of time on this problem, and I'm about ready to go berserk...
Hello. I've been using Session Manager for a long time, but lately, it's been causing a problem that's been driving me out of my skull, and I think I've finally pinned it down to SM. lately, when I've tried to load sessions, even with a small number of tabs, it's caused my internet connection to drop, or, at least, to slow down to the point where pages try to load, but finally come back with a message that the connection timed out, or the page had took too long to respond. I have my Windows Vista Home Premium computer running Firefox 11 connected via Ethernet to a wifi router that is connected to a cable modem. I tried disabling pre-fetching, resetting my router to factory settings, I tried a different router, I tried removing the router and connecting directly to the cable modem, i tried a different modem, I tried disabling the Symantec extension, I tried clearing windows' DNS cache, I tried disabling Firefox's DNS cache, I tried disabling Symantec's Firefox extension (I have Norton anti-virus), and I tried disabling my anti-virus & firewall programs (hmmm, did I leave anything out?), but none of that solved the problem. I haven't noticed this behavior with any other program, and Firefox goes along swimmingly otherwise. The reason why I think I've finally pinpointed it as SM is that trying to load a certain 9-tab session caused this problem multiple times, but I eventually got it all loaded correctly, and then I tried restarting it, and Firefox's own built-in feature of loading the tabs and windows if it closed properly the last time worked just fine, and it loaded quite quickly.
So, why might this be happening, and what can I do about it? Do you think it might be a matter of the SM data being corrupted/ If so, how do I get rid of it? I found the Session Manager Export Tool extension and exported my sessions and then tried uninstalling and re-installing SM, but it hadn't gotten rid of the old SM data. Please help, as I consider SM to be a vital part of my Firefox and have come to rely on it, plus I'd like to be able to use my old saved sessions again. Please help ASAP, too, as I've already wasted an unbelievable amount of time on this and I am extremely frustrated and aggravated. Thank you.
The response I received:
"Session Managwr cannot cause your Internet connection to drop, it simply doesn't have the ability to do that. All it can do is cause Firefox to restore tabs that have been saved. It can cause lots of web pages to load, which could slow down Firefox or possibly your Internet connection (if you have a really slow connection), but it can't drop your Internet connection. The only exception to that that I can think of is if your modem has a web page with a reboot button and you press that, then save the session such that restoring the session causes the reboot button to press, but that is extremely unlikely.
By default Firefox loads tabs one at a time anyway so it's unlikely to slow things down when loading sessions. If Firefox can restore sessions properly, the Session Manager should be able to do so as well, since Session Manager uses Firefox's restore capabilities.
I'd recommend disabling plugins in Firefox and/or other addons and see if that helps. If you can figure out what changed recently that would help narrow things down.
As for Session Manager data. It doesn't store anything other than the sessions. You can delete those if you wish."
My reply:
Well, I have a cable internet connection, so I don't think speed is the problem there.
Are you sure about Firefox loading only one tab at a time? I know when I load a session, it seems to show several tabs loading at the same time, and I can't remember it ever not being that way.
Frankly, though, I need more specific, targeted help than being told to just start randomly disabling extensions. I've ALREADY wasted an INCREDIBLE amount of time on this and am ALREADY EXTREMELY frustrated and aggravated, and to just go blindly shooting around in the dark at random is only going to throw craploads more wasted time and aggravation onto the already huge pile. I'm at my wit's end here. I can't take much more of this. I need REAL help. I need more specific, targeted advice about what sorts of things I should be looking for, what sorts of things I should be trying, etc. I don't have any patience left to just start flailing around randomly and likely getting nowhere fast.

Answer 1

Hi,
You can try to verify that '''Don't load tabs until selected''' is enabled in '''Tools''' ('''Alt''' + '''T''') > '''Options''' > '''General'''. [https://support.mozilla.org/en-US/kb/Options%20window%20-%20General%20panel?as=u Options > General]
[https://support.mozilla.org/en-US/kb/Options%20window Options]
If the problem persists please also check in a [https://support.mozilla.org/en-US/kb/Managing-profiles new profile]. If the new profile is okay, you can later [https://support.mozilla.org/en-US/kb/Recovering%20important%20data%20from%20an%20old%20profile?s=profile&r=1&e=sph&as=s copy the needed personal data] from the old profile and start using the new profile. You can then delete or troubleshoot the old profile. Firefox stores your personal data and settings in [http://kb.mozillazine.org/Profile_folder another location (profile folder)] separate from its [http://kb.mozillazine.org/Installation_directory folders/files]. A new profile would have the default Firefox settings in '''Tools''' ('''Alt''' + '''T''') > [https://support.mozilla.org/en-US/kb/Options%20window Options] and [http://kb.mozillazine.org/About:config about:config], and usually would also be empty of '''Extensions''' and themes ('''Appearance''') in '''Tools''' > '''Add-ons''', and their settings. Also, a new profile would have no previous stored website cache/cookies/data/preferences: '''Tools''' > [https://support.mozilla.org/en-US/kb/Clear%20Recent%20History '''Clear Recent History'''].
[https://support.mozilla.org/en-US/kb/Profiles?s=profile&r=2&e=sph&as=s Profiles Howto]
[http://kb.mozillazine.org/Profile_folder_-_Firefox Profile Folder & Files]
[http://kb.mozillazine.org/About:config_entries about:config Entries]