Mozilla Thunderbird pre-68 on Slackware -current?

I have just upgraded my laptop to -current, and this has brought over Thunderbird 78. For the past year I have been battling to get versions of Thunderbird past 68 to some sort of usable state, and I have failed. Both on Linux and Windows, they randomly freeze, silently reject ssl certificates with no error messages, break all sorts of add-ons. It is just not workable. Whatever architectural changes have happened after version 68 (I think), have made Thunderbird unusable. Currently on this laptop, version 78 has completely broken TBSync - so I can't do any sort of contacts or calendar sync with the backend. Even worse, if I try to enable it, it completely freezes the entire machine when composing an email message - and I have to do a hard reboot.

Is there any way to get a version of Mozilla Thunderbird somewhere between 60-67 working on Slackware -current please? Either to compile it, or a pre-compiled package which works on current.

I have tried to use the scripts from Slackware 14.2 and current to compile version 60, but I get the errors below. I have tried to install the binary for 14.2, but that won't run.

When trying to compile with the scripts from 14.2 and sources for Thunderbird 60.9.1, I get:

Code:</snip>
thunderbird-60.9.1/test.mozbuild
thunderbird-60.9.1/moz.configure
thunderbird-60.9.1/.yamllint
client.mk:72: *** client.mk must be used via `mach`. Try running `./mach build`. Stop.
And with scripts from current and sources for Thunderbird 60.9:

Code:50:49.80 Compiling url v1.6.0
50:52.68 error[E0713]: borrow may still be in use when destructor runs
50:52.68 --> /tmp/thunderbird-60.9.1/third_party/rust/url/src/form_urlencoded.rs:261:40
50:52.68 |
50:52.68 259 | impl<'a> Target for ::UrlQuery<'a> {
50:52.68 | -- lifetime `'a` defined here
50:52.68 260 | fn as_mut_string(&mut self) -> &mut String { &mut self.url.serialization }
50:52.68 261 | fn finish(self) -> &'a mut ::Url { self.url }
50:52.68 | ^^^^^^^^ - here, drop of `self` needs exclusive access to `*self.url`, because the type `UrlQuery<'_>` implements the `Drop` trait
50:52.68 | |
50:52.68 | returning this value requires that `*self.url` is borrowed for `'a`
50:52.68
50:52.81 error: aborting due to previous error
50:52.81
50:52.81 For more information about this error, try `rustc --explain E0713`.
50:52.88 error: could not compile `url`