Thunderbird 45.2.0 Constantly Crashing

I have Thunderbird 45.2.0 Portable Apps version installed on a USB2 device that contains a SSD drive.

I run Kaspersky A-V on Windows 7, both fully updated. I have no plans to install Windows 10...ever.

When I load Thunderbird off the PortableApps Launcher or even by directly executing the "portable" wrapper exe, the program starts to consume memory...and eventually lots of it.

I have documented Thunderbird consuming as much as 3.6GB of memory according to Windows Task Manager. At these levels it may or may not crash, but it is so darn sluggish to the point where changing to the app sometimes shows up as "nonresponsive" in Task Manager.

As part of the troubleshooting process I have checked the following:
- mailbox size: around 600MB total
- total apps folder including mailboxes: abot 700MB
- loaded the app with and without addons enabled, no difference
- as far as I know none of my addons are on Thunderbird's "troublesome addon" list
- checked the size of various files suggested by Thunderbird's online troubleshooting guide: all within appropriate sizes
- checked the size of contacts: about a 100 or so
- checked for GoogleMail usage: never used it and don't have any accounts configured for it in Thunderbird
- checked number of mail accounts configured in Thunderbird: 2 and they match the 2 access methods to my email provider
- checked for any IMAP accounts: none configured
- tried using Thunderbird in both "online" and "offline" modes and seen the same extreme usage
- checked Thunderbird "activity log": BLANK...seriously
- checked Thunderbird "error log": constantly recurring error every 6-7 seconds regarding chrome://messenger/content/tabmail.xml, saying "TypeError: tab is undefined"

The "error log" message about "tabmail.xml" never stops...ever...it's constant. I ran a Google search on that error and it seens like the Thunderbird developers have been kicking that one around for about a year now, assuming I read their Bugzilla entries correctly.

Addons installed: Adblock Edge, CompactHeader, Disable "You", ShowFolderSize, ViewAbout, ShowInOut, Saved Password Editor

Even with every addon removed from Thunderbird it still consumes large amounts of memory and acts very sluggish. The "error console" output also does not change regarding the "TypeError".

I have tested Thunderbird with no extensions installed and my A-V protection completely disabled. No difference to the massive meory usage by Thunderbird nor it's sluggish behavior.

I have completely reinstalled Portable Thunderbird without extensions and the "memory hog" issue has not gone away. So I decided to add a few selected extensions to make my Thunderbird usage a bit friendlier to me, and no change.

Having these apps in a "portable" format, and having no viable portable alternative of comparable quality, is important to me since I am not always in a position to lug around the same piece of desktop hardware everywhere, AND, I do not trust "cloud crap" (what a security hoax that stuff really is, assuming you take the time to really look at it).

Any ideas? Anyone?