Firefox insists to be default browser ...

[Miroslav Skoric <skoric@uns.ac.rs>]

Hi all,

After the recent upgrade of Firefox and Thunderbird in oldoldstable 
(Mate desktop), about a month ago or so, when the versions changed from 
60-something to 90-something, Firefox annoyingly keeps asking me to be 
the default browser, even though I always respond to that asking by 
click on 'dont ask me again', and have set it as default browser in 
Mate's Control Center default applications.

Furthermore, Thunderbird is also set there as default email client. 
However, if I click on a weblink in Thunderbird mail, another 
Thunderbird session opens (instead opening Firefox). And when I close 
both software, and return to Mate Control Center to check again for 
default applications ... voila ... Thunderbird seems as magically 
selected itself for web browser too (both with mail client)!

How to prevent that misbehaviour? All worked well for me with older 
versions of Firefox and Thunderbird (before that version jump to 90 
something). What went wrong with the new versions?

Misko