Fallback to Chrom(e|ium) if the Firefox driver for selenium isn't available

[valholl]

Installing the selenium driver for Firefox under Debian is a bit of a pain, so when trying to run the tests locally I've found it easier to change the code to fallback to the Chromium driver if using the Firefox one fails.

As a Firefox user myself (for everything else) I would consider it extremely reasonable if this PR was refused, but I felt it was right to submit it in case it was useful for somebody else.

[codecov-commenter]

Codecov Report

Attention: 5 lines in your changes are missing coverage. Please review.

Comparison is base (36d882d) 70.33% compared to head (cd9045f) 70.25%.

Files	Patch %	Lines
src/bepasty/tests/test_website.py	37.50%	5 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##           master     #317      +/-   ##
==========================================
- Coverage   70.33%   70.25%   -0.09%     
==========================================
  Files          44       44              
  Lines        2623     2629       +6     
==========================================
+ Hits         1845     1847       +2     
- Misses        778      782       +4     

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[ThomasWaldmann]

Thanks for the PR!

Good to have it if it makes life easier for some developers.

Chromium should be rather ok as it does not have the problematic components which Chrome has. But for automated testing use I guess they would not be that problematic anyway.

[valholl]

Thanks!