You have control. The spacing issue is described at https://support.mozilla.org/en-US/kb/new-thunderbird-45#w_mail-composition

This page should have showed in THunderbird when you updated to version 45

OK - I can live with the line spacing - although it will be a pain, but what about the hyperlink following on to new lines?

sunnysewsit said

OK - I can live with the line spacing - although it will be a pain, but what about the hyperlink following on to new lines?

Sound like word wrapping:

try this:

email yourself or whatever and save as a draft open the draft in view pane (with & without view source) does it look fine in the viewer if so its a artifact of the composing window.

As a saved draft, the following line still is a hyperlink, but I can highlight the text following the hyperlink and then choose Format-remove links and it will take away the hyperlink, but I don't think it should work like this

The hyperlink being continued onto the next line is a reported bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1273655

It's a Firefox bug, and sadly Thunderbird uses the same code.

As a workaround, make sure there is a space after position where you're going to add/paste a link.

You can work around most editing issues if you're familiar with HTML. There is an add-on "ThunderHTMLedit" where you can correct any fault HTML that normal editing has produced.

P.S.: As was already said, you can switch off paragraph mode as described here: https://support.mozilla.org/en-US/kb/new-thunderbird-45#w_mail-composition